I don't think it's that at all. The real cause is just some entirely institutionalised academics wrote the textbooks and everyone else is copying it rote as if it's the way of doing everything because that's all they know.

You need people from outside the echo chamber. I found The Open University to be a considerably better education provider on that basis than the red brick I attended quite frankly. The material and tuition is far far far better.

Incidentally your point in Khan Academy is spot on. That's basically OU but the material is miles better and it actually leads to a qualification.

Example free course: https://www.open.edu/openlearn/science-maths-technology/intr...