While I understand the benefits of ferated servers, I think the inherently fragmented nature of the infrastructure is the biggest hurdle to the adoption of (for e.g.) Lemmy and Mastodon as replacements for Reddit and Twitter.

There is an extra layer of complexity, and the less tech-savvy users who want a simple process to follow diverse communities across many instances are going to run into issues. That group likely comprises the vast majority of potential users.