An interesting article I saw (from 2019) describing the potential intrinsic tendency for decentralized platforms to collapse into de facto centralized ones.
Author identifies two extremes, "information dictatorship" and "information anarchy", and the flaws of each, as well as a third option "information democracy" to try and capture the best aspects of decentralization while eschewing the worst.
It's certainly a great read and is worthwhile, however I fundamentally disagree with the base premise that the goal of a federated system is to be uniformly distributed.
Why should an instance focused on a niche topic have the same representation as a general instance? Why should either have the same representation as one with abhorrent content?
Choosing your instance is effectively a statement that you agree with the mission of the particular instance. The number of low user instances demonstrates that there are a great number of people that share the author's vision of federation.