I suspect the economics of gyms might be such that if it was pay-per-use they'd either have to charge insane rates or go under. It's not so much that consumers like monthly fees as that the gyms like them because they're easy to forget about.
There are gyms that charge per use, the fees may appear higher but if your dedication to exercise doesn't turn out the way you planned you will be money ahead.
For the best chance at getting a payment plan that doesn't count on you having low motivation to exercise, look for locally-owned independent gyms, avoid the Bally's and other franchise/chain operations.
This isn't good advice. The locally owned ones are often even more desperate and willing to go the extra mile to defraud you. The idea that small businesses are more honest than big ones is a complete myth. Most of the time it is the reverse: big corporations have more to lose.
The advice to go local is less about it being a guaranteed win and more about it being how you find those who will go above and beyond everything.
I've actually never heard anyone say "The advice to go local is less about it being a guaranteed win and more about it being how you find those who will go above and beyond everything."
Instead I always hear a dogmatic something like "support local business! Big corporations are evil!" When I've actually been defrauded out of FAR FAR FAR FAR more money by buying local.
(Also, I do go to the gym)