Do you have them listed *super extremely unmissably obviously from space* as INTERNSHIPS? They may just be looking at dates and thinking that you aren't good employee material because of short stays.

I love people who don't READ the resume "You only have ONE job on here, that's not much job experience." "Did you note that it was 4.5 years?" "Oh no, I didn't... let me look a little more" Dur? (this was an actual experience a few years ago)