I could see the gyms not wanting people to use the bikes. After all, a lot of them pay good money for the bikes themselves. The tri-pedals alone are 99 bucks a pair, and the newest Johnny G bikes are 1700 bucks. Revmasters are about 1200 bucks, StarTracs are about 1400- 1600 bucks, and Schwinn bikes are about 1200 bucks. That's a lot of money they plunk down for the bikes.
Also, gyms have maintenance contracts with the companies they purchase bikes from. Some bikes have strict warranties, and if the company found out that the gym violated their contracts, the warranties would become voided, and then the gyms would have to pay for their maintenance. That could cost some bucks. The alternative solution is just lock the doors when the classes are not in session and don't let anyone in to use them.
Koffee