This.
Being a private pilot is like being in pee wee soccer. Everyone gets to play regardless of ability, you just have to be able to tie your shoes. Commercial flying requires a certain amount of ability, and versatility. A 1-2 hour preflight is extreme. Not sure if you are including planning into that number such as weather, cross country flight planning etc. but I can't imagine somebody, even a new student spending more than 30 minutes touching the airplane. Is this student being forced into the commercial by a family member or something else? Could be the student just isn't into it.
That's not correct, that is the purview of Pt 103 and LSA/Sport Pilot. PP is already selective on medical criteria which includes exclusions for flawed mental function.