Chrome's automatic updates and the power it holds on the web
One of the realities of the modern web is that in general browsers hold pretty much all of the power to dictate how the web develops; it's (currently) browsers that decide what features to implement and what features to deprecate. In practice that means that Chrome (with its fairly dominant browser share) holds the power, including the power to abruptly deprecate things. But as I was thinking about this, it occurred to me that a large part of this power rests on the widespread use and acceptance of Chrome's automatic updates to itself.
Browsers mostly can't move the web forward (for better or worse) without changing themselves. This means that a limiting factor on the speed of changes to the modern web is how fast new versions of browsers can propagate. If you make a change to your browser and it takes a year to get into the hands of 50% of your users, you can't change things on the web very fast. If you can get it into the hands of 80% of your users in six weeks, suddenly you can move a lot faster.
(Both Firefox and Chrome can somewhat change their behavior without a full update, by remotely turning on feature flags or being opted in to previously inactive changes or whatever, but in general many shifts require actual updates.)
Chrome both releases frequently and tries very hard to automatically update itself. This combination drives changes in Chrome into wide use fairly fast, and in turn that is part of what gives Chrome its power on the web; if the Chrome developers decide to do something, they can make it fairly pervasive fairly fast. That gives their changes weight that the changes wouldn't have if they took months to make it to 20% of the (desktop) web.
(Based on looking at stats I could find with a casual Internet search, it looks like new Chrome versions take only a month or two to hit peak usage and then decline rapidly, which is roughly what I'd expect from their general release frequency. Chrome is apparently planning to transition to releases every four weeks, which will drive this even faster.)
PS: Of course automatic updates for browsers have important primary purposes, like promptly getting security improvements into the hands of users. But I'm sure the effects on getting general browser changes into widespread use don't hurt in the eyes of the management that has to fund all of this.
PPS: My understanding is that mobile browsers are somewhat different, especially on Android, and may update more slowly. But desktop browsers still do matter for many people and there Chrome auto-updates on its own schedule.