A lot of these people come from south of the south of the border. They try to claim asylum, but there are rules to that. For it to truly be asylum you are only supposed to move 1 country, you don't get to pick and choose. You cross the border into the next country and file for asylum, and that is either granted or not.
They'll let these people in and in 5-10 years grant them citizenship for crossing illegally. Wash, rinse, repeat.
KC