Viewed through the lens of "what will cause the most bad publicity" a browser is understood by 90% of the population. The "fediverse" isn't. It can be spun to cause damage in the way a browser cannot.

Google don't care about the federated stuff because it's not big enough to bother them, in fact it probably siphons all the crap they'd rather not index off to a place they no longer have to worry about.

They care about bad publicity and being seen to implicitly support "bad" things via their app store.