I've sent out some of those emails. Most don't respond. Others told me:
Funding is limited
My GREs are preventing me from getting any serious consideration (apparently most clinical applicants who make it at that school are above 80th and 90th percentile)
They didn't think it would be a good match, even though they considered my application one of the strongest (this is another school, i'm guessing they didnt emphasize the GRE as much.. I didnt do poorly on it, just didnt get above 80th)