Probably many registered users started out unregistered - while they are deciding whether they wish to continue, or they know they will never make more than 'one or several edits' so it is not worth signing in.
Even if one has an account - it may be convenient to make the minor change directly without signing in.
As a general response - try creating articles on some of the middling/more obscure relevant topics, and perhaps overview articles.
I don't know if mine is the same problem - but the the 'features' that did appear on the right hand side when editing an article have now moved to the top (various wikia wikis). Looking at Special Preferences there is nothing obvious to change it back. If it is 'a mistyping that rearranged things' how do I return the layout to what it was?
Can anyone tell me - which other wiki-hosts use a layout which looks like Oasis (the actual wiki-programming does not matter for this purpose).
As the vast majority of wikis readily accessible use a layout that resembles that of Wikipedia 'there must be something to it' (and not just because of WP).
One problem with blocking specific IPs - a library public access system which goes through a single IP (though many computers on a number of physical sites), so there could be several Wikians operating autonomously. (Somewhere on WP there is (or possibly was) mention of a case of two persons who 'for whatever reasons' were having a disagreement but happened to be using the same IP.) Vandalism and 'trivial wiki-graffiti' will always exist - and should be treated as an entirely different thing to the 'right to be forgotten' otherwise complications are likely to arise.
Given that the Oasis layout is what most people encounter on coming to a Wikia wiki how many people who would have been on Wikia never actually signed on and discovered the WP-like skins were available?
Advantages of Monobook would include - it looking like the vast majority of wikis elsewhere in the Wikiverse (even if the actual underlying 'programming etc' differs between them). As a long-standing WP user there have been considerable parts of the Oasis 'activities' that are not intuitive.
Are there any statistics on how many Wikia users are 13-16? 'At a guess' they are likely to be concentrated in (but not confined to) certain areas of wikiadom (and more likely to be responsible for certain types of wikispam). However it will be impossible to calculate the numbers accurately - if a young person does not so self-identify and writes in a mature manner (even if colloquially) they may not be spotted.
In other contexts I have found that there are a surprisingly large number of even reputable bodies which have #not# contacted me about my details to show that they are GDPR compliant.
If 'they' can allow Monobook to be used by some people solely on their IP or other geographical location and others are blocked on those grounds, it is a form of discrimination.
As I said above 'Wikipedia-style layouts' do appear to be the norm across the wikiverse, so some compromise could be worked out.
Many Wikians use pen names - so the connection could be forgotten (closing the account and 'changing the patterns' of IP use and language style on re-signing in etc): what about the 'real people' being described on Wikia pages ('X said something off the record' etc)?
Questions Have there been any requests for vanishing (especially given the number of Wikia-pen-names under the new legislation? As across Wikia there are 'a fair number of pages' relating to living persons (including those alive at the time the article was written) - have there been any requests for information to be removed with loss of visibility (rather than ordinary deletion)?
If the rest of the world can access something that is legitimate but those parts of Europe which are supposedly free and open are deliberately blocked then there is a form of discrimination - and there will always be 'clever persons' who can work their way around such things.
If 'those in charge' had stated overtly some time ago that for technical and practical reasons it is not feasible to sustain two skins and Monobook was too ancient in programming terms people would probably see the logic.
But given that Wikipedia, Ganfyd, Rationalwiki and 'a myriad others' can sustain the MB-style - it would have been possible to create a new skin (with options) that suits both sides.
Given that 'many' other wikis use the WP-like set-up the presence of Monobook should not be a problem - and excluding European users from accessing one format when it is available elsewhere would be overt discrimination.
Also - given that 'live people whether or not based in Europe' will still appear variously in Wikia (eg authors, actors, TV series/film directors, actual persons mentioned in passing...) and there are many users active on Wikia from around the globe, the argument is flawed. Should any mention of a living person be deleted - and should we all be 'Anon + number'?
Wikia should have an obvious link to 'If you wish to call in the Right to be forgotten contact us...' - and why aren't we being bombarded with new messages 'You have a new message on X-wiki: do you wish to be associated with your contributions here?' - covering even the most trivial tweak on a random wiki found while exploring the Wikiaverse?
Can someone tell me #any# wikisites other than Wikia which have the Oasis set up? The vast majority have a Wikipedia type set-up (whatever they individually or collectively call the skins). Wouldn't Oasis be just as old and problemified (to coin a word) as Monobook - why not create something new from scratch - including one that has the best bits of the WP-layout and Oasis/where certain aspects can be personalised to make the wikipage look more one or the other? How many of us MB users would accept some 'ads round the edges' in order to have our prepared set up?
I am not a techie - but what is the connection between Monobook and GDPR? Why couldn't 'they' just send a message to everyone 'follow these steps to confirm your details and you are happy for us to keep them (and do 'this' if you want to change them)'?
Given that they had decided to withdraw the Monobook skin 'a while ago' it should have been announced - and help provided for those needing to change over (and even making changes to Oasis if need be).
I think the main issue is that the plug was pulled without any warning to Wikia users. Whatever the issues with Monobook and GDPR 'singly and in combination and whether or not affected by other factors' there should have been a 'this is going to happen - how do Wikia users wish to develop things' discussion.
Given that 'many other wikis' can support a Wikipedia-like layout, and the GDPR regulations have been working through the system for several years it would have been possible to make arrangements to suit Monobookers (some at least of which might also suit Oasisers).
Many people use wiki-pennames, and there are tens of thousands of abandoned wikis on Wikia which will have to be dealt with.
Most people accept that 'things change' and 'major reformats occur' (and 'three weeks later one wonders what the fuss was about) - and would have no objection to confirming their details etc.
I have tried using the Oasis skin - but found a number of problems: I cannot see what links to page X or where to delete it (should I wish to do either) and, when going through entries in a category, which I have already looked at.
What about those people with visual and other issues who actually need a plain black and white website?
One and One's might be logically appropriate for IPs and other number-names.
And 'girl' could be considered patronising by some (given that Wikia users have to be 13+ they would #probably# be 'young adult' (as book classifications etc go) or 'adult'): and some real names 'change gender according to the region'/can be applied to either gender (Daryl, Kim, Vivian etc).
One possibility '(Wikia-name)/IP' on first use and then 'this user.'
It appears that there is no particular convention/obvious use for the present: but it is appropriate to consider the possibilities.
This is meant to be an open-ended question - such as are occasionally necessary to decide whether the answer is 'continue with the existing usage' or deciding that an alternative usage is preferable/useful.
That, in one sense, is the whole point: if one does not wish to make assumptions, and wishes to use something other than 'they and them.'