If that kosher gym were more affordable to most people, perhaps they would go. But to be perfectly candid, if one is a Yeshivish, Kollel couple, perhaps the money that the wife is working so hard to earn, or the money that the Shver is generously giving them (so that his eidem can sit and learn and not worry about parnassah), could be put to more practical use than working out in a gym. There is PLENTY of exercise to be had without going to a gym.
Frankly, I think it would be better for the marriage, if the couple would take daily long walks together or even have their own workout routine that they do as a couple in their own home. It would give them both exercise AND together time. There are plenty of books about how to exercise properly. Much cheaper than a gym, for people who cannot afford a membership.
And yes, as we take note especially this week, the Greeks were way too into the perfection of the human body. It behooves us to remember that the first Gyms were from Yovon, and as Jews we focus beyond the physical. They focuses SOLELY on the physical.