One quick comment:
For a lot of legal jobs or internship, there are way more apps than spots available. There are way more apps than the employer can feasibly interview. There are way more apps than the employer can comb through. It's not an exact science, but the employer or the person whose job it is to go through those apps is going to do anything they can to thin the pile out. For different employers, there are different ways of doing this.
Such as:
Only hiring from top schools, only hiring from schools that lawyers at the employer went to, only hiring people they personally know, only hiring people with very high grades, only hiring attractive women or fratboys, randomly picking apps out of a shuffled pile, whatever, etc.
Maybe none of this is fair, but it happens in reality. I can tell you right now there is nothing you can do to change it. You just have to make the best of your own situation within the system.
With the big firms, a lot comes down to marketing and justifying the high billing rates to rates to clients. They say, "well, our billing rates are high because we have to pay out huge salaries to recruit the best and brightest young associates and retain the most experienced partners." To some big corporation, best and brightest simply translates to Harvard et al.