I've never had that many issues with mentors. When you do, it does stand out though. I just think this is survivors bias and people remember the bad encounters more than the normal ones.

The vast majority of mentors I've played with these past 4 years are just silent. That's like 90% of them (and we're talking hundreds if not thousands of encounters). The idea that over half of them are bad is an absolutely ridiculous claim. They're just there and do their thing. If you ask they will give advice, but otherwise nada. Every now and then some idiot is an ass and that's that. Every now and then you get a really good mentor with a welcome message and endless patience, and that's that.
All the others know better than to give unsolicited advice and stay quiet (if you're a mentor that cares to help others you know exactly what I'm talking about).

Your mileage may vary depending on your datacenter and probably personal skill as well. But honestly there's no way the situation is as grim as many make it out to be. It's all survivor bias.