The nature of high school students now is that they begin specializing in certain sports or activities earlier and earlier. Parents are convinced the only way their kids will play at the varsity level is if they focus them in on a single sport. Students used to be able to play 3 sports, sing in choir, be in a play, and still be a good student.
The truth is that they could still do this, but parents have become convinced that their kids have to specialize. It's too bad and I think baseball has taken a bigger hit due to this than football or basketball (partially because parents see their kids getting scholarships in football and basketball, but not baseball).