That said, what I do think helps here is that Kbin has a much lower barrier to entry. I find it much easier to sign up on here than trying to determine which Mastodon instance to use and I think that helps tremendously.
Kbin is technically federated and Kbin.social is technically just an instance on a federated network, the federation is just broken right now. But the simple fact of that not being a consideration, and everyone signing up on Kbin.social, has led to comments like this where "it's so much easier".
It rather proves my point; putting decentralised whatever front and centre makes things pointlessly complex and offputting to end users. They don't want to think about this shit, they just want to read stuff and post. The less they have to think about this shit, and/or the less this shit has an impact on their experience, the better for them.