SSA runs a small ad in the PG/HG magazine, PG/HG pilots are of course aware of the existence of sailplanes. I think pilots are not crossing over because they don't want to. It isn't cost, I would guess the majority of PG pilots that I've met could afford sailplane flying. Probably more HG pilots that switch as they are used to the pain of rigging and having to sort special transportation(roof racks instead of trailers.) Besides I'm sure HG pilots would rather disappear to the sailplane field then switch to PGs and fly in front of their old HG friends.
Changing hobbies also involves an ego barrier that can be a large hurdle, if you have been doing a hobby for ten years even if you are just OK at it, you have some standing and credibility(perhaps less then people think, but it is real to them.) Switch hobbies and you go from knowing the ropes to being the know nothing new guy. A lot of people's egos cannot handle that. As for getting them in the door Pimping FAST certificates isn't going to do it, the motivation isn't there. Maybe if you took a lesson from drug dealers and gave the first one free you might hook some converts. I went from sailplanes to PG makes me laugh how the various disciplines score converts. Such a nice reaffirming data point to your chosen chariot when someone discards what they are used to and joins you.