Two points here:
First, a college professor has a very different relationship with students than HS teachers. I only have about 50-70 students a semester, but many faculty in other disciplines have 300. We only see our students 3 hours/week for 15 weeks, though some do come by office hours. HS teachers see students 5 days a week for 36 or 37 weeks, and the teacher and student spend all those 5 days in the same building together. HS teachers should know their students in more complex ways than a professor. When I write letters for college students, I review the syllabus, their written assignments, their small group activities, progress in the course, etc. With the occasional exception, I can only write about their academic work narrowly defined.
Second, letters of recommendation have always been a joke, though it is getting much worse. If a recommender does not rave, then it isn’t worth writing the letter at all. I write this as someone who has read hundreds if not thousands of reconmmendations and reviews of the work for UG, GS, and faculty. Anything that seems faint praise condemns the candidate. I wish it wasn’t so, but from Lake Woebegone, all my students are above average, even brilliant (and I bet that gets the righteous going).