A gym I joined years ago required a certified letter sent to their headquarters.

I think it's a public service to tell young people how gyms work. Basically it's high pressure sales ("this discount membership offer only good for today!") plus hard to cancel memberships.

Gyms work on a model of human nature + oversubscription.

Human nature means that a huge % of people join the gym, go two weeks, and never return. Then it's hard to cancel, so the same people that don't bother coming in, don't bother figuring out the membership cancellation gauntlet.