It's just really really not safe man. Lots of people breathing heavy, sweating etc in a confined space. It would be a Corona playground.
And believe me, of all the things that have shut down that have effected me the worst it is definitely the gym. I hate it, the gym is my favorite place outside of home. They have the weights I don't have at home to properly grow muscle, not to mention I feel like I'm more focused working out there and that doesn't even begin to touch on the mental benefits I get from lifting/working out (I feel like that part gets overlooked).
I stopped going about a week before they actually shut the doors just because I was starting to feel really uneasy about the possibility of virus transmission. Since then, I can visibly see less muscle mass (not just post-workout pump), I don't "feel" nearly as strong and my mood is kind of down from where it normally is. Admittedly the mood thing could be just as much to do with Corona stress in general but I feel like it would be lessened if I had my normal routine.
All of that being said, it's absolutely the right thing to do to keep the gyms closed right now. I couldn't think of a much worse place to be open to the public at this time. I'm doing what I can with body weight exercises, walks at the park, treadmill at the house, but it's just not the same.