Do you think most adults are mentally and emotionally stable, absweetmarie? Our country's current use of anxiety medicines, anti-depressants, sleeping pills, and drug and alcohol abuse tell me there are an awful lot of hurting people out there. Back when my youngest was in a playgroup, I learned I was the only mom there who wasn't on anti-depressants or sleep aids. From the outside, these women seemed together but obviously some of the them were struggling emotionally.
Frankly, one pattern I see in some teachers is that they have unfinished business from their own time in school. Sometimes that comes out in who they favor and who they don't. There is a phys ed. teacher at our high school that all the kids say picks on the athletes. They claim she isn't really athletic and was probably teased by some jocks when she was in school or something. So can you see how that person could become the kind of coach who has a grudge against the talented athlete and looks for every way possible to promote the untalented ones to the former's detriment? (We aren't talking about a normal encouragement of all types of students, but an over-the-top thing.)
One of my son's teachers told him he had really wanted to go to the school S got into, but couldn't. He was cold to my son after that point in time. Many people are small, petty, and trapped by their past. Sometimes they are the ones making the stupid rules.