What my DCT told me and some training directors have said when I talked to them about it, some sites will do a cursory review to reduce the applications and reject a first round of apps that are obviously not a good fit (not enough hours, not the right kind of training, etc.) and send out those rejections. Then they do a more in depth review of the remaining "short pile." Individuals that get rejected from the short pile may seem like they might not be a good fit for other, more specific reasons such as mismatch between your career goals or something. From what I've seen, the first rejects will be a mass email, then they might send a personal email for rejects from the short pile with a more personal explanation of why you were not considered a good fit for an interview. I had a few of those before I had to withdraw for health reasons last year. Hope that helps!