I wouldn't say it's the focus, I would just say that is one of the basic requirements to make he team. Is it important or valuable to baseball at all? Probably not. Is it going to force kids to get in better shape for when they show up for tryouts in Feb? Yes. I would go as far as to say the time likely doesn't matter and the coach is saying it to get the kids running and in shape.
As for the coach, I don't think he expects better baseball players from a timed run. Whether a kid is a better college prospect is really none of his concern either. The odds are that there are plenty of nonathletic kids who can't do 2 miles in 18 minutes and he wants to get rid of them before having a weeklong tryout where those guys are taking reps away from borderline players.