This is factually wrong, and disproven by the fact there are now fully independent federated instances such as BlackSky and soon to be NorthSky. Furthermore, they have independent codebases which are fully compatible. Compare to ActivityPub where most instances are just running Mastodon or some close fork or risk breaking compatibility. What's the point of federation if you are stuck with a monoculture of implementations?

The main BlueSky services are still by far the most popular, which is why we see centralization on the network.