@jwildeboer as a long time AP dev there is a long story about why we are at such a position of fragmentation we are right now and we at Lysand started to call it the "Mastodon situation"..
Here a citation from a unpublished version of our webpage:
The Mastodon Situation

It turns out that if you write a fully compliant ActivityPub server, it's not going to be able to federate with any of the major instances. This is because the base specification is not very useful, as it is missing a lot of features that are necessary for a modern social media platform.

For example, Mastodon has a feature called "custom emojis", which allows users to upload their own emojis. This is not part of the ActivityPub specification, so if you write a server that is fully compliant with the specification, it won't be able to display custom emojis.

In fact, Mastodon has diverged so much from the base specification that it becomes very difficult to write a server that can federate with it. Some issues caused by this divergence are sometimes not even documented, leading to unexplained errors.

Complexity

Another issue with the Fediverse/ActivityPub is that it uses complex data structures that are difficult to work with, such as the JSON-LD format. This in turn makes it develop to create new software that integrates with the Fediverse.


Thats why I joined a collective effort to develop Lysand as alternative, easier protocol to Activitypub, with tooling that makes it completly compatible with Activitypub using a Compatibility layer, because this fragmentation really hurts the community and the fediverse as a whole.