This may be a site oriented towards gaining, but personal decisions people make about their body -must- be respected. Not everyone tries to constantly gain, some take a break, some stop...
But yeah Love These Curves is/was a site that didn't seem particularly sexually engaged, so it might be worth a look for some whenever it comes back up.
Heck many just want to gain to a certain point and then stop. Not to mention people's weight can plateau as well. So people demanding "gain forever" do need to rethink that approach.