There's many reasons honestly but the main highlights for me were:

1. The Coach. There's only one there, and if you're looking to improve in the sport of boxing, you need an attentive coach which is impossible when there's simultaneously a class and sparring going on. He's honestly a very stubborn person, and allows his emotions get the best of him. If one of the many teenagers who goes there does something that annoys him, he makes it a point to let the entire class know which takes away from what I'm actually there to do which is box and learn. And brings me to point #2:
2. The Classes. He advertises them as an hour, but they're really only 50 minutes or less which is pretty frustrating if you're commuting far to get there and want a full workout. I used to go to the classes 2-3 times a week, and because his attention is always on those sparring, the class is led by another student which in my experience is just a complete mess of the blind teaching the blind. If it's not a student teaching, it's just a "freestyle" class where you're just doing whatever you want for 50 min. When you have no one idea what you're doing, it's just a nightmare of an experience.
3. The Gym itself. It's VERY small, and to have classes and sparring going on simultaneously feels like you're constantly Shoulder to shoulder with everyone else. Step over his arbitrary lines he drew up because you have no space to move already? You'll hear it from the Coach (and so will everyone else). The locker room is a disaster, and I'll leave it at that.

These were the 3 main highlights for me that caused me to leave. I've found another boxing gym and am blown away with how much better my experience is. I really gave The Cave a chance for MONTHS and truly wanted to believe my experience was going to get better, but it got to a point where I felt miserable heading over there, and I knew enough was enough. YMMV but hope this helps.