That's simply how the underlying ActivityPub system was designed. It was intentionally designed around instances, not users.
In ActivityPub the system is centralized around instances. They are the core unit.
So things like account transfers are sort of irrelevant to the core protocol. Why, the protocol would ask, would anyone want to do that?
We could do better. But the designers of the system decided to go a different direction.
This is one of the reasons some people are optimistic about Bluesky making better choices.
@volkris
“So things like account transfers are sort of irrelevant to the core protocol. Why, the protocol asks, w(sh)ould anyone want to do that?”
This assumption is giving me prototype-inheritance deja-vu. This is ask-assuming, “why should people move ISPs or web servers”?
An ActivityPub *streaming* server instance can be defederated or stop operating & shutdown. Instances are ephemeral, people are not.
Servers provide compute runtime, access, distribution & moderation of users content.