I think gyms have a liability factor with the spin room. A lot of gyms don't want to be responsible for what might happen to a member if they're spinning on their own in the room and something happens with the bike. Other gyms don't want a member to accidentally damage a bike, so they would lock the doors to prevent such accidents from happening. Theft is not a big factor in a gym... it's about the liability.
My gyms keep the doors open, even the gyms where I pay money to work out. But they let me use the rooms, it's because they know I'm an instructor, and generally, they know instructors will either be practicing to teach a class or use the bikes to stay in shape, etc., so they let us use the bikes without giving us hassles. That's part of the reason why I got certified.
Koffee