When I last tried to sign up, they requested a phone number, I assume as some sort of an attempt to make it harder for spammers to sign up. I don't think they have any legitimate reason for that sort of information, so I didn't provide it. I don't remember the specifics, but either I couldn't finish creating the account, or it was created and then automatically locked/suspended a few minutes later. The end result was that I couldn't sign up and use the service in any meaningful way.

I don't know if that's still the case or not. After that rather awful experience trying to sign up, I've lost all interest in trying again.

I'm not surprised they're having trouble growing when they impede the ability of people to sign up! There's no reason for their signup process to need anything more than a username and a password. They don't need my email address. They surely don't need my phone number or any other information about me.