I think the key here is that it’s a feed managed by the user. There’s not enough commercial potential in that. As a tech company, you want to be the one curating the feed, and you want the user to believe you’re doing it in their best interest so they don’t notice how you’re making money by subtly feeding them ads.
RSS is simply too good for the contemporary internet.
Well, the ones that federate with Meta will still be federated with those who don’t. So it’s really no different from what the Fediverse is already: Fragmented by design.