Monero is not a "major" coin.

The top 10 or even more top 5 coins do well with their own forum. We're not even close to that now.

The traffic will organically migrate to more specific forums when XMR is big enough that most (or even a meaningful portion) of its participants are not primarily BTC participants, just as it does with major coins. I doubt there are even a handful of such people now, if that.  There is no need to force anything.