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Seriously, joining Mastodon is not particularly difficult; people just freaked out a few years ago at being asked to pick a server to join. The joinmastodon.org website has gotten a lot better at explaining what that means and just directing people to mastodon.social if they don't want to pick something more specific, but the "oooh, this extra step makes Mastodon super super scary, if you pick wrong YOU ARE DAMNED FOREVERRRRRRRR" vibe persists.
The other challenge that AP has as an ecosystem is that they have been hostile to anyone wanting to build an index or business. People need to eat and they turned off a lot of developers who'd love to make their living building social media tech outside of the corporate oligarchy.
ATProto welcomes all, even if there is the occasional drama or hostility.