Can't say I've met too many Jazz/Blues teacher's that have this kind of a reputation, but on the Classical side, I've meet a few.
These teacher's usually only have 1 or no children of their own. So, fortunately or unfortunately, don't really know, or better, don't care to know kids. There mind set is on being the number #1 teacher of all their peers! A lot is at stake for them. Prestige and prize winners! They get the students and the respect from the parents with waiting list an arm long!
To add, some of these teachers aren't always obviously mean on the outside, (some are, yes) like yelling at the kids, but a lot of these teachers are mean mentally and that's how they work their magic. These mean teachers usually have a time frame. Mentally they have mind games to get the student to practice more and more. They have an agenda which is to get these kids to finish their ARCT by grade 9 (Age 15) or sooner! With the parents help, they usually get them to their mark. But at a price!Hours and hours of practice, and very little social life.
Here's where I see the problem. There are winners and loser. The winning students are the ones that "get the gold ring" at the end. But God help the ones who don't get the final touch-down at the end of their piano experience. Has to leave a mark!
For the ones who succeed, they are the ones getting the standing ovations at the concert halls!
I guess they can brag about having a teacher that was a "Son of a Witch" with a capital "B".