User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-28455010-20201030230054/@comment-1038387-20201031003035

Polls and WikiActivity were not removed for insufficient use.

Polls were unreliable, prone to breakage, couldn't be edited, easily gamed and apparently a security risk.

WikiActivity was no longer considered necessary, because Recent Changes was improved with Enhanced Recent Changes and Filters and whatnot... so they thought. It's since become clear they did not anticipate use as an at-a-glance patrol for iamges and categories added, or that RC is too cramped for some neurotypical users... but it's not coming back. There's a dev script though.

The old editor wasn't ported because why would you? If you buy a new car, you don't install the seats from the old one just because they were comfy. It comes with seats.

The Category Exhibition one is correct. Google reads the pagination as duplicate pages, which inflates page count and diminishes SEO score. It was a great feature, but overtaken by developments from outside.