>And at every layer except for maybe the PLC directory, there's nothing stopping anyone from fixing that “almost nobody does” problem.
If there's nothing stopping anyone from fixing a problem, and yet nobody fixes it, then there's something is stopping them.
Might not be a technical impossibility, or a gun in their head. Could be as simple as inertia or addiction.
But saying "the problem is totally solvable" just because there's a solution available, is pretty naive. Solutions have costs themselves, and not all are created equal or equally feasible.
A relay or appview needs a ton of resources. Blacksky finally created the second ever real-world usable appview instance after 2.5 years.
Also, the open source version of the appview doesn't work at Bluesky scale. You need a proprietary database for sufficient speed.
AT Proto is completely decentralised, except for all the structural and financial points of absolute centralisation.
Or people don't think it's a problem!
Maybe there are a ton of people who joined Bluesky because twitter devolved into a room-temperature-IQ right-wing hell hole, not because they cared about federation or whatever.
Everything has trade-offs. Again and again people choose centralized services because they are a better product.