The task of how to scope sites — whether to split or combine subjects — has been one of the more difficult philosophies to flesh out. We constantly make adjustments as we learn exactly what makes a site "work" and what causes them to falter.
At the most basic-basic level, Chess and Poker became sites — or at least they became eligible for further consideration — because they rallied the enthusiasm and resources required by Area 51 to give them a shot. But it takes more than sheer numbers and a definition move from proposal to site. We do a thorough review of leading proposals to evaluate whether they have a good chance of working well with our existing network based on a large variety of considerations.
If you read through the blog post:
Unix and Ubuntu: Why Both?
…there's an underlying concept that a site is not much good to a group of users if they will not show up. It was generally thought (I'm not going to debate this point here) that perhaps Chess was a subject unto itself — that there was potentially a substantial group of users who wouldn't identify themselves as a "board game enthusiast" and this site would be of no use to them. The same basic premise for Poker.
Whether that turns out to be true or not is still a part of this trial by fire. They initially earned the right to try through Area 51. They've since navigated successfully through a private beta to, essentially, where they are right now.
To date, neither of these sites have made substantial inroads into the massive chess and poker communities respectively. But then again, the Board & Card Games site hasn't had much success attracting these audiences either. So for the time being, we're watching to see if their ideas (i.e. their premise for having a separate site) pans out.
There's no indication that the existence of either of these sites has substantively held back your progress — nor is there any indication that combining their audiences here will substantially create any sort of additional network effects to move the needle much either way. But subsuming those sites is a disruptive change to those community that goes against the precepts of
Does this site have a chance of succeeding?
Whether you agree with their existence or not, they've earned the right to continue to make a go of it.