User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-1905698-20150519203506/@comment-126761-20150519222710

To clarify our intent: we want to provide a stable article layout across many devices, so that when users edit the article, they know it will work well for all their users. The issue we have found over the past few years is that, as screens diversify, many visitors are being left with increasingly difficult to read pages.

We don't blame users for this - but it's a side effect of making edits on an article size that is considerably wider than what a pretty significant number of users actually see.

There are other important benefits as well, such as around line length readability.