> Someone told me I was rejected because of high test scores. I didn't really believe them, but it kind of makes sense.

Armed forces does a lot of tracking and they need a mix of people. It makes sense to try to get people into jobs that work for both the person and the seevice, and where the person is likely to stay (if the service wants you to). Marine infantry is an important and prestigious job, but it might not be something that would have kept your interest.