There is also no reason 100% of the population must have university educations.
Wrong. A more intelligent and knowledgeable populace is always preferable. Higher education also tends to go hand in hand with general kindness and well-being of societies.
I know a lot of unemployed people with higher education and two higher education who consider themselves too educated to work as a janitor or cashier. Immigrants do not have this feeling, it's cheap labors
Yes, they consider themselves too educated to work as a janitor or a cashier -- again,
because there are immigrants and bydlos to do the work. I can guarantee you that these jobs would get done if they paid 10,000 euros a month because nobody would be willing to do them for less. And then you would get people who'd do it for 9500€, and then some who'd do it for 9000€, until the supply meets demand and the pay and amount of workers stabilizes. Basic Ricardian economics.