Great question. 

The ethos surrounding Btc is decentralization, rules over rulers, sovereignty and ownership (hold your own keys). I see all of these attributes in nostr.

Unlike bluesky where you have decentralization in name only, and mastodon where each server is run by an all powerful human admin who can ban at will etc. 

That said bitcoiners are the beachhead in large part as Jack discovered and shared nostr over a year ago. There are non-bitcoiners on nostr, it is just a bit of work to find them.