@kino @admin @anderscs right, they can't force, but they could implement features that could effectively break federation with them leading to other platforms to either having to implement the feature or be left with a perceived "fault". and perception matters.
the other side is a platform holding a lot of users and/or public awareness of ActivityPub can also hold back development of the project by not implementing things, this has happened again with Mastodon, but I think other platforms have got bored and are just implementing things anyway now