A new twig to the branch of theory on PTs. Training with other people is more fun. Training 121 is the most fun. Once you've trained 121, everything else is boring. This is maybe the reason why a drop-off in training frequency follows PT sessions?
Or maybe it's the lack of personal responsibility. When you "give up" the responsibility to a PT to decide what you do, when you do it, you lose the accountability the rest of the time?