Yep, sure a lot of 'coiners here, that's true. But I would argue that the ones here are potentially the most sane ones. Not trying to sell you shit you don't need and just kinda talking in their own bubble - thus, easy to navigate around; at least I think so.
Diversity here is not (yet?) very high, but it can only build by inviting people here. It's like in a relationship of sorts - someone has to take a step :)
Discoverability of no-coin stuff is currently not that good - but mind you, Nostr is, out of the three you listed, by far the youngest of them all. Mastodon is actually quite an "old" project (and ActivityPub as the protocol) by now - I think it started 2014-ish?
Give it time, a bit of your attention, and an invite to friends. Help it move out of the crypto bubble, actively. :)

Just my two cents as a guy who came here while having a massive depression due to the state of the "internet" (Reddit and Twitter going shitfuckingexpensive API calls - and especially Twitter locking features and falling into an identity crisis of its own whilst Facebook Threads was a massive promise with little to no delivery; aside from being cucked in the EU) and looking for a new "home". Been here since, seen dozen zapathons (after i missed them, ofc, cuz timezones are bitches x.x) and a lot of meme worthy moments (#beardstr being my favorite - penis butter my second followed by bullshit instead of bullish). The software people write is amazing and the fact that it takes nothing but a few basics to implement is INSANE (minus needing this one random bitcoin-based curve and bech32 encoding... small details but eh).

I see a great future for Nostr - but, it needs legs to walk. ^^