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.)