There is a powerful network effect to overcome here, and I don't think "being federated" is enough to overcome it for most people. Reddit and tumblr and discord offered us "what if all your forums/blogs/chatrooms were in one place" which is massively convenient, and why people flocked to those platforms. Thats a transformative user experience. being federated is transformative, but the change to the user experience -- beyond a larger barrier to entry -- is minimal. The point of mastodon is that its functionally equivalent to twitter without being centralized. But there are no decentralized places left on the internet, beyond those holdouts who are either very attached to their old technology or want to maintain their unilateral control over their platform, and who are unlikely to federate.