Why is that?
I have worked professionally as both a designer and developer, and find many parallels between two. In my opinion, my very best programming work has been code built from my interface designs. The design process allows me to have an intimate understanding of the application flow before I write a single line of code. I find working from the designs of others never allows that same level of understanding, leading to a codebase that takes longer to make great (which, in business speak: longer = more expensive).
Thinking back, I started on my path to designer at around the age of five, and started learning to program around the age of ten, so I have a lot of experience in both fields. Perhaps someone who doesn't start until college simply doesn't have enough time to become proficient in both?