One of the other issues is lack of adequate high school preparation. One of the factors I saw in college (15 years ago) as a Physics major was that a lot of students that wanted to study physics (or other sciences) just didnt have adequate foundational knowledge coming out of HS. If a year of remedial courses is required just to get to the point where you can take freshman level classes, it becomes very difficult to complete the coursework required for the major, because many of the courses have to be taken sequentially. You can't just load up on a bunch and take classes in parallel to catch up. If you start a year (or more behind) or try to switch into the major late, you can't finish in four years.
Humanities major fields seemed more tolerant of lack of preparation - one could switch into them late or do some remedial work before diving in deep and still get the required coursework done because courses did not depend as much on one another and could be taken in parallel.
It's very upsetting, though, to be told you can't study or have a career in the subject you're interested in because you lived in the wrong district when you were 13 years old. I don't know if this is a problem with high schools, colleges, or both, but it was a large factor in choosing my own major.
Humanities major fields seemed more tolerant of lack of preparation - one could switch into them late or do some remedial work before diving in deep and still get the required coursework done because courses did not depend as much on one another and could be taken in parallel.