I certainly understand why various sites, including mainstream and social media sites, dropped their RSS feeds, but it's never made sense to me why browsers did (especially when browsers have so many features). It seems to me RSS is good for the web and therefore good for browsers.

That said, the UX of RSS was pretty terrible compared to social media. I think it could have been different—podcasts managed to make RSS mainstream and with a bit more tuning and standardization it probably could have worked. I really think the issue was that in the 2009-2015 period huge amounts of industry mindshare went into mobile apps and social media and RSS (or its eventual successor) were left half-baked.