Having immigration illegally exists because legally it is not possible for some people. You can't just accept 100k people all at once, you accept 10k of them which is a nice number, then what does the other 90k who can't get accepted do? I am not talking about not accepting criminals, that exists too, you look at the application and background search shows that he was a criminal so you reject him and that person illegally immigrates anyway, that happens and that's bad.

But, if we are talking about just because of numbers? The others who would have been accepted if they were in the 10k but just stayed out because of numbers, would immigrate as well. This is why USA will always have this issue without a doubt for a long time.