Interoperability is great, but sadly there isn’t really any organized group effort to standardize more aspects / extensions of ActivityPub. AP is really “thin” in that it barely prescribes anything. There’s not even a test suite to test whether software complies to the spec of AP.
So everyone kind of does their own thing, and fixes interoperability on a case-by-case basis. This makes it kinda frustrating to spend time on - lemmy already has special cases for many different softwares (peertube, mastodon, …) and every one increases the complexity.