What exactly is the problem with just focusing on everyone? Indeed, it might turn out that the cost of "focusing" is actually more than the added cost (if any)

What exactly is the problem with just focusing on everyone? Indeed, it might turn out that the cost of "focusing" is actually more than the added cost (if any) of providing the universal service. I personally wouldn't want to be the one to tell some bright kid that they weren't allowed in because they're the wrong demographic. I had enough of that as a kid.