Simply put it is because in the US the quality of teachers is fairly low.

For those of you who haven't down voted already I can explain why this happens:

Its a low paying job, the only reason to go into teaching is passion. Its great that folks are motivated, but that doesn't make them GOOD. Plenty of people pursue careers in art and music and fail, few people who pursue teaching get pushed out by "better" teachers.

Give someone a tool that lets them take the easy way out and not have to exercise critical thinking skills and this is the outcome you get.

This might be surprising to some. But many people are simply not highly motivated by money. Sure, some amazing teachers simply can't stick with teaching because it doesn't pay enough, but a lot make it work.

10 years ago, at my university, I remember there was an opening for an English associate professor. They had over 300 applicants. I guarantee you there were lots of amazing teachers in that group because they certainly weren't doing it because of the $38k starting salary.

Ontario has teachers that make 100k+

Quality was still horrible when I was in highschool.

The average is probably more important than the extremes. In my field (radiography) the range is large, and also fairly meaningless. In the small group I do pay sheets for and with the same qualification, the lowest paid is on approximately 1/6th that of the highest paid.

100k is the average

https://www.blogto.com/city/2020/09/average-ontario-teacher-...

Oh wow.

'Those who can, do; those who can't, teach.'

An absolutely horrible, horrible message. The worst part is that this sentiment creates a self-fulfilling prophecy.

"Those who can't teach, teach gym"

Either way, false negatives are quite high too, all it takes is some prompt magic. Most AI detectors assume AI written text maintains a consistent format and style. Unless there's some probabilistic signature tied to one specific model, there's no reliable way to check that doesn't make the error rate too high for it to be reliable.