A number of instances defederated from it because… well, the reason a number of people are here is to not be on Reddit and seeing a mass deluge of content ported from Reddit defeats that purpose. There other other reasons too, like the fact it makes a ton of submissions and each has very few if no comments leading to the impression of a very barren community.
As long as websites/advertisers see their visitors as using a Chromium based browser they will continue to target for Chromium, regardless of whatever front facing UI is used.
The inherent problem is Google has an outsized voice in Chromium’s developmental trajectory, and any major changes to Chromium will have downstream impacts, whether in actual implemented feature sets or forks making continued modifications on top.
The best way to protest is to not use a Chromium browser. Switching from Chrome to another Chromium browser is at best a side grade; everyone using Chromium is subject to Google’s whimsy.
Pragmatically it doesn’t matter if Microsoft chooses not to implement it; as long as Edge is on Chromium, Google can leverage this to continue to bully the web to their own devices.