More people start an undergraduate education than finish it. If you're only looking at people who got through the system, you've already filtered out a number of those who have low motivation or low ability.
More people start _anything_ than finish it. Since starting is a prerequisite for finishing, it is always the case that a maximum of 100% will finish, and likely fewer.
If your point is that more people start school than finish and somehow that weeds people out, you could also say the same thing about apprenticeships.
If your point is that more people start school than finish and somehow that weeds people out, you could also say the same thing about apprenticeships.