They won't give you a reason for denial. Honestly, don't even think of it.
Best advice I can give (and I know this isn't what you are asking about, just a general shout out to others applying) is to expect rejection, and always think of a way to improve your package.... Maybe retake the ASTB, improve your GPA, get some flight time, join a club or organization, take a leadership role, volunteer for something challenging, anything...
Don't look back if they say no... Don't even give a sh*t or look down on yourself, just look to the future... "How can I make my package better?"
Don't take no for an answer. If you want it bad enough, you will get it; so long as you DON'T give up.
I had to apply 4 times before they finally gave me my flight slot.