It actually doesn’t.

Install the official Mastodon app on your phone, launch it, scroll past the instance selection box that railroads you to mastodon.social anyway, and it’s no more complicated than Twitter. It’s just that nobody knows that.

Fun fact: The official Bluesky app has a selection box for a PDS, too. It’s no more and no less complicated than the official Mastodon app. Nobody knows that either.

Granted, of course, if you let yourself be railroaded, the place where you land in the Fediverse won’t be the bee’s knees, and you won’t know that there are not only better Mastodon instances (or more Mastodon instances in the first place), but also better server applications than Mastodon (or anything else than Mastodon in the Fediverse in the first place). But hey, it’s easy-peasy.