At $10 per month, they're showing desperation to keep the doors open. I'd be willing to bet their profit margins are next to nothing with overhead being EXTREMELY high surviving off leverage and constant borrowing. Be interested to see their P&L. Seriously, who would want to train in an uninspired library?
the answer's simple: people who don't want to go to the gym.
planet fitness actually has a brilliant model. they're a gym for sedentary people. they court people with self esteem issues by focusing on the friendly, welcoming atmosphere, and at ten bucks a month even when people barely go they think "it's only ten bucks, i might as well keep it." so they have gigantic membership rolls but if you actually go into one you'll see a ghost town.
then, to make it even better, you can only cancel the membership in person. so someone who already feels self conscious about themselves isn't going to want to walk into the gym and talk to the attractive person at the front desk and explain that ten whole dollars a month is just too expensive or that they're so damn lazy they can't justify the price of two cappuccinos.
TBH i love planet fitness because it keeps all the people who have no interest in exercising corralled into one place rather than taking up space at better gyms.