I suspect they are trying to be polite.
I have now heard the Bluesky CTO state why they didn't go with ActivityPub (at least) 3 times.
Each time, the wording was a bit different, but the message seemed to be the same.
He gave one technical reason, and one social reason.
Given how much time they spent developing their protocol, I suspect they could have solved the technical problem (in much less time).
Which just leaves the social reason.
Which I suspect is the actual reason.