There are usually limited acting training opportunities in college drama programs if you're not one of the students consistently cast in your school's shows. Don't worry! My experience with actors who received their BAs in theater is that most of their real growth happens after college when they get out in the world and pursue new opportunities for expanding their skills or simply find the industry more impenetrable than they imagined.
Sometimes there are good reasons why you may not be getting cast. Sometimes it comes down to your physical type. And a good deal of the time those of you who aren't being cast may simply not be smiled down upon by a certain teacher or you may not be in the right clique.
Not to worry. When you're not cast, keep doing whatever you can to learn about the industry, to find ways to fill in the gaps of what you can't get in your college program and consider working with a coach before your school's next round of auditions.
The most talented woman at my college was never cast in a show. She just wasn't identified as being "in the club" so to speak. I think about her work frequently as she was more real, more intuitive and more connected to honest acting than any of us.
How much you're cast in your college program is actually not very indicative of your future success. Do not be disheartened.