A lot of shipped code is effectively unmaintained even on pages which are otherwise being modified, in many cases by relatively non-technical people (a small bu

A lot of shipped code is effectively unmaintained even on pages which are otherwise being modified, in many cases by relatively non-technical people (a small business owner contracts a webdev to build a page and show them how to update the content, for example). And in a lot of cases it's not obvious that your code is going to be incompatible. For example the most recent case there was code which was like `function foo(x) { if (x.group) x = x.group; /.../}` where that function was being called with `foo({ group: [...] })` or `foo([...])`. That code breaks if `Array.prototype.group` is added. No one is going to figure that out themselves unless they test on a version of a browser which ships `Array.prototype.group`, and empirically no one does that. Yes, we could find a way to break fewer pages than flash EOL broke. But even just a handful of pages people actually use is too much. No browser wants to ship an update which will break (to pick a relevant example) the website of the government of Brazil, even if they somehow "ought to have" updated their code before that update. Developers are empirically not going to do that update and browsers are not going to punish the users of the pages of those developers by breaking them.