I just don't like to be in a browser for things that don't have to be. At least not for things I use regularly, that don't have to be. My computer has a window manager for a reason, I can move windows all over the place, and things like email I can keep always visible at work, or keep minimized and out of the way at home. But in a browser, the limited impact of tab groups aside, I'm pretty much stuck with a flat organization structure that can quickly become burdensome.
I don't think they're necessarily against federation with others, now that I think about it more. We're just content for them, to promote the endless scroll for their own users to get trapped in.
I imagine they see a world where ActivityPub is meant for federation between services from the likes of Twitter, Meta, Google, and other big players with maybe a large open source project that gets defanged.
Let's do congress next.