* Simply attending a 4-year university has costs beyond tuition and books; there are plenty of people who don't go to college because they can't afford 4 years out of the workforce.
* The 4-year university system is extremely brittle, in that it creates good outcomes primarily for people who are in the right place (somewhere they can easily attend a good university) at the right time (right after they graduate high school) --- do anything to get off the college track during your high school years and it becomes extremely hard to re-engage with it.