Just the same as why some people have to study constantly and others only a few hours per night.

Some kinds of information connect to previously learned information better than others. Knowing Latin helps with medical body part names.

Some degrees have coursework that overlaps other course work heavily. (Math, basic physics, and static mechanics all overlap a lot.)

Some material is more “rational” and can be calculated, others depend upon rote memorization.

Some study techniques work better for sone material and some people than others. Be certain to try many techniques.

Some people are smarter than others. A benefit of being smart is learning fast. A hardship is crap study skills.