A personal trainer I had at a very low rate (about $35/month in 2015) Manhattan gym confided in me that the place had something like 10X more active memberships than they could ever fit into the gym, even if everyone came at a uniform time distribution once every other day. They knew empirically that they could basically get away with overselling a service (adequate time and space to use the facility) than they could actually provide, because as the article says, most people just come 3 or4 times and then give up, but they've already signed up for a yearly rate.