[DubaiSis]

If you sit down with yourself and really think through what happened, you can probably come up with a few reasons on your own. No, nobody is going to point blank say this or that was wrong, but think about a few things.
Grades, meh, good enough or good? Good enough might not have been good enough when cuts have to be made.
Appearance. You don't have to be a beauty queen but you do need to look put together, stylish, clean, etc., and then that undefinable something. Stated bluntly, do you dress weird, sloppy, ugly? Again, you don't have to look like you're falling out of Vogue, but if you say "I'm going to dress the way I like and to hell with what other people think" well, you got what other people think.
How was your conversation? Did you talk enough? Too much? Too loudly? Weird subjects? If they have to make cuts, that weird girl who talked about aliens would be a pretty easy cut.

Once you have really thought about that, you might be able to assess where you can make changes. Being part of a sorority IS to an extent about fitting in. If you want in, you may have to adjust some things about yourself. Or, if on critical thought you decide you'd rather dress like a biker than be in a sorority, then that's good too. You do you.

I wish you the best of luck moving forward.