I've seen that problem too, but there's nothing we can do about it with the tools available to us. I think the main problem is the AIs are somehow forced to build cities as close as possible -- typically with 3 tiles of spacing between cities. They will break this rule only in very rare circumstances. I think the "stuck at 1 city" situations are when they have no good city spots with a 3-tile spacing from existing cities. The only thing I've found which significantly affects this is how much they value tiles already containing their own culture. I fiddled with some settings to devalue self-culture within the first 2 rings around a city site, which is why they place cities 3 tiles apart (1 tile of no-culture between). The modding community had a big investigation into AI city placement a few months ago. No one conclusively found any xml variables that control AIs willingness to place cities at further distances to grab specific resources. The code to control this is most likely contained within the c++, which we don't have access to.