As the owner of a CrossFit gym, I can also verify this. Our business model is built around getting people to show up to the classes, and in any given week we have around 90% of members showing up. In one of the larger gyms (24hr, Lifetime, Gold's, etc.), you're looking at closer to 10%. The main difference in costs is the trainers though, since every class is closely coaches and led by experienced instructors.