I guess I consider Apple Pay via Wallet, which I use, to be different from Gym Membership via Wallet, which just doesn't seem worth the effort? Maybe I'm unusual.
In a gym context specifically: a lot of gym wear doesn't have pockets. Being able to leave your phone and physical wallet at home or in a locker and use your watch (which you also use for workout tracking) for every membership card swipe, vending machine electrolyte/protein drink purchase, and gym class ticket can be very convenient.