That's a result of the chicken and egg paradox. People aren't joining because most content is centered around bitcoin thus no diversity, and content isn't moving away from bitcoin and becoming more diverse because people aren't joining.

i wasn't even aware of any bitcoin relation. i've just joined nostr hearing about it as a sort of fediverse type thing but not reliant on an instance host so there's less admin drama - so far that's been my biggest issue with fediverse