Could it be because logistically it's not easy? I don't live in a place as big as SoCal or anything, but I went through a phase trying to learn wrestling from actual wrestlers. There aren't really classes for adults to go learn wrestling. Maybe there are in some places, but unless you're at an MMA gym with a dedicated wrestling class, what's the next best option? Trying to find a local college or high school that would let you work in? I'm not trying to be a smart ass. I know the top level BJJ guys could probably pay money and hire some wrestling coaches for private lessons, or find good wrestlers that do BJJ also and bring them into their academies, but I've always thought it was difficult as an adult to find a lot of serious training with serious wrestlers.