Humanities teachers assign grades that are based on the students’ work, not based on how well they did compared to their peers. I haven’t seen their rubrics, but I’m confident they exist. The difference between those grades and some STEM grades is that an 87 average in humanities is an 87; it doesn’t change based on work turned in by fellow students like STEM grades apparently do.
That was the point – some STEM professors assign grades to individual assignments and all the grades in the class are low (40% or less). At the end of the semester the professor may decide that 35-40% is an A, 25-30% is a B, etc. The grades aren’t based on mastery of the material, they’re based on how well students did compared to their peers, and there’s no clear standard for what constitutes a particular grade. I don’t think either of those creates an environment conducive to learning.
If professors are incapable of creating exams that accurately reflect what they’ve taught, perhaps they need to go back to college so someone can teach them how to write better ones. Other colleges’ professors don’t seem to have that problem, so there must be classes that are useful for learning that skill. If professors learned how to write good exams consistently, there wouldn’t be much need for a curve.