The most likely reasons he didn't get into Caltech are probably: 1. Caltech is a lot smaller than most of the others, only admitting a little over 400 per year

The most likely reasons he didn't get into Caltech are probably: 1. Caltech is a lot smaller than most of the others, only admitting a little over 400 per year. 2. Caltech puts more emphasis on producing researchers than most of the others do.