To be fair PACE with the limited exposure to gliding that I have it is the Pro Pilots who are quite happy to go IMC in gliders.
It might be because they really arn't bothered about going onto instruments. Even the very experienced plain gliding instructors will shy away from it unless they have to ie come down through a layer.
Get a serving Mil pilot or commercial pilot who instructs gliding on their days off they just use what ever clouds they can to get lift. They will happily spin down through it, poke into doing loops etc.
I would agree with Mary that the majority of glider pilots don't as a habit fly in IMC because it scares the !!!! out of most of them.