They might be good at covering it up. Or you're not actively looking, and so it's not in your sphere of awareness. Or the coworkers to whom it's happening don't trust you enough to discuss the problem with you, and so it's not in your sphere of awareness.

I'm a pretty average straight white dude, but I have seen this happen, right in front of me, at multiple jobs, and absolutely nothing happened except when I spoke up and started something over it. The targets didn't say anything, because the power imbalance (real or perceived; I tend to think the latter, but then, I'm not the one being attacked and made to feel powerless in the first place) was too great.

Unfortunately, child abuse is, in fact, rampant among musicians. Want to try a different argument?