An issue is that #ActivityPub was more or less designed centralized around instances, for better or worse, so ideas like SSO or other ways of using accounts across instances is a bit incompatible with the underlying technology.
There are ways to kludge it on, but it wasn't designed with that objective.
This is one area in which other systems like #Bluesky might be better, having made their different engineering choices in their cores.
Yes, I know many people feel that way.
I'd rather have a more functional protocol that better provides features so many are clamoring for, better serving those users, regardless of associations.
@volkris @chartier I much prefer #activitypub, warts and all, it has huge issues, but it's a free protocol under our control. #bluesky? not so much...