Because if the training time arranged in a day is too short, the gym will not have much profit. Moreover, the number of students in each class is not fixed, and it may be more or less, but a gym without group calisthenics is definitely not enough (the rotating spring bed is also a group class).
There are three forms of health clubs. The first is the gym in the hotel, which generally has a swimming pool, but it is small in size, expensive and not popular enough, mainly for hotel guests. The second is a membership gym for middle and high income groups, with advanced equipment, complete courses and strong coaching team, which is generally popular. The third type is the mass fitness club, which is relatively low in hardware and software, but very popular.