Not enough people here (it's a network effect) and it's way too complex to sign up.

My signup process was like this:

• After going through the list of servers, I had to pick one of them. As someone who went through that whole situation with XMPP, I know that this alone is enough to make most people turn away.
• Then I picked beehaw, because most of the communities I wanted to join were there. The signup form turned out to be an application form. I spent about an hour mulling over what to write there.
• Since the page told me that if I didn't hear anything back after 24h, I could consider my application rejected, I wrote another account application at feddit.de after waiting for about 48h.
• The feddit.de account was approved, but I only noticed by my login working a few days later. I didn't get any notification. That's what I'm using right now.
• After more than a week, I got an email that my beehaw application was accepted.

I don't know anybody with even half as much patience as myself. Every single step on this way would have been a dealbreaker for a regular person by itself. Creating an account on reddit takes a minute, not a procedure of several days.

Also keep in mind that most people don't understand what federation means in the first place.