If there were more girls touring down here there might be a bit more of a market for them.
I don't know the area that well, but I'd have thought it might be the other way round?
Pembrokeshire has half the population of Swansea and a larger area (so lower population density which is presumably mere evenly distributed?). Swansea would seem to be a more obvious choice for a touring girl as far as easy access to a larger pool of potential punters goes.
Its also going to be further (more time/expense) to get to than Cardiff or Swansea and Wendy has already mentioned accomodation costs. Lack of anonymous city centre hotels and apartments might make it more difficult to find workable accommodation as well?
I'd have to say that we don't get all that many brilliant tours in Cardiff. There are some very good regular visitors, but a lot of girls that I'd like to see swerve Wales completely and concentrate on the likes of Manchester, Birmingham and Glasgow. Wherever you are, the grass is always greener somewhere else

Is there anything we can do to encourage girls to come this far west?
You could always try contacting them and asking? I've had luck with that in the past. My booking fee covered her travel and accommodation (I also gave a couple of recommendations for reasonably priced workable hotels), and she was happy to take a chance on getting a few more. If there are a couple of you down west that could get together and make advance bookings that might swing it?