I’m saying this without knowing anything about your gym. But in my experience. There are often more guys than girls who work out at a gym. Guys are more likely to go to the gym more often, with a set routine and put in some work.

Where am I going with this? More guys, who sweat more, use the shower and thus it becomes dirtier, quicker. Simply due to there being more guys that use them. And then it starts to smell more. Especially, when the staff doesn’t clean the showers very often. And doesn’t do a very thoroughly job either. Dirt and bacteria accumulates as a result and stink up the place.

the fact that you’ve experienced this at multiple gyms, I don’t think is attributed as much to guys shitting in the shower, as I would say it’s the multiple gyms that are consistent in not cleaning their showers.

The gym I go to have a sheet inside the locker room where the cleaners sign off every time they clean the toilet and showers. According to the sheet, they do so regularly, and by the cleanliness of both the showers and the toilet. I believe them.