I understand it fine. I just don't like it.
Obviously, different Mastodon instances don't have shared credentials. Which means that whenever you visit a different instance in a web browser, it doesn't know you, and thus you can't just follow someone, or have your preferences apply to the page, etc. It's unlikely that this problem will ever be solved, given the nature of the protocol, and given that it hasn't been solved yet.
I'm not ideologically attached to federation. All I wanted was an alternative to Twitter. I found that attempting to migrate from Twitter to Mastodon was unpleasant. I expect that other people — not everyone, but many — will feel the same way, which limits Mastodon's adoption.
> Mastodon is developed mostly by volunteers rather than a team of well paid UX specialists
I can sympathize with their lack of resources while still not wanting to use Mastodon myself.