There are "gyms" and there are "gyms"
I belong to a huge gym - the dues are low and there are lots of machines and classes for working out - if I wish to have one-on-one instruction with a trainer, I pay extra for that - and it is not cheap!
In my town there are gyms for the wealthy where you always work exclusively with a personal trainer who puts you through your work-out. This is expensive.
Gyms can be real cash cows and really rake in the money. It is a true business and takes some brain power to run successfully - just like ay other business.