By their very nature, rogue servers for MMOs we’ve lost are not going to have the population of the live game. They’re inherently smaller. And I’ve seen more than a few people who have, say, stayed out of City of Heroes’ various rogue server options specifically because they feel much smaller than the original game did. This is not a game that requires huge parties to clear things reliably, but for some people the smaller size is just going to be a dealbreaker.
Still, there are a lot of things that can turn one off from a rogue server. Maybe the server in question is home to a community that’s just off-putting and unpleasant. Maybe the developers have gone in a more solo-focused or group-focused direction you find unpleasant. Heck, maybe the sign-up process involves agreeing that enchiladas are superior to fajitas and you’re not willing to accept that. What does a rogue server for a departed MMO need to grab your attention? What makes you determined to jump in and play the community-led continuation of an otherwise sunsetted effort?