It all comes down to money. If professors make the subject hard, they don’t get students. No students is less money for the University and less opportunity for the professor to scope out potential thesis candidates.

There are some professors who make it hard. Generally those who have tenure don’t care and put down a shitload of work on students. Also, if you have a well funded lab that pays well you will have a lot more students willing to deal with a harder course.

Normal students want to zip thru and get to living. It’s sad - but its a tragedy of college being so expensive. It’s hard to take a risk on academic (mis)adventures that can crater your financial standing for life (yup for life - student loans cannot be written off during bankruptcy).

In Europe it's no different, except we mostly only pay with time. Even without the "motivator" of student loans, most people enter university to party, pass tests and get out with paper that grants them access to better-paying or more interesting jobs. Learning is incidental.

I think that despite it being less obvious these days, it's still true: actually learning for the sake of knowing and understanding is a nerd thing. Even at universities, students who care are considered weird.

Why learn complex stuff when you can zip thru coursework and party with friends, and get laid every week with different chicks, away from parents’ watching eye?

For a teenager with bursting hormones this becomes a trivial choice

Widely true, though as an undergrad in the US I (fairly unusually) wrote and orally defended a 120pp anthropology thesis; as a Masters student in England I wrote a 40pp thesis that was worth only 20% of my overall marks, but sat in an exam hall and handwrote essays for three days (for 70%) while being proctored by a fellow in a robe wearing a sword... In general my British peers were better-spoken and better-read than most American students, but not actually better academically I don't think. I don't think most education produces consistently good results, but it makes a space for some people who are motivated.

It's how most exams and tests work and the emphasis on those (rather than learning) being the goal ruining it all.

American universities definitely have their great courses, but the fact that so much depends on money, makes teachers focus on funding first, publications second and teaching is very low on the priority and so is actually making sure students "understand", rather than "know".