sure, that might partly be because they have no intention of monetising user content, but a lot of it is naïveté.
Like, you don't have any corporate veil protecting you, and you're not doing anything to make your users give you legal permission to, say, store their posts in a way such that they might end up being mirrored on pleroma.lolicon.expert? That's… …reasonable, if all of your users are laypersons! But the moment you get an actual business of any sort or even just a particularly litigious person using your site, you're taking a big fucking risk.
There're ways these license clauses could be written way better, absolutely! Because a lot of them are broader than they really need to be! But most social media platforms that are neither some average tech nerd who doesn't realise that everything they own and 30% of their income for the next forever might be at stake if they fuck up hard enough, nor a company that can drop tens of thousands of dollars on getting a better TOS written (+ about that much on versions for different jurisdictions, translations, so on) and then thousands more every time it needs any updates, are probably going to go for extremely broad boilerplate.
But yeah, no, Mastodon instance admins risking basically unlimited liability because they're assuming good faith from everyone are playing a dangerous game.