Exactly. The utility of income is not linear. The first 10,000 dollars are much more useful than going from 190,000 to 200,000 a year. That's why the tax system has a progressive structure. If you want me to work 10% more then you need to pay me more than 10% more.
And that does not even consider that my free time is very limited. If I have say 2h of completely free time everyday (24 hours minus work, commute, chores, gym, household crap, etc) and I need to work just 1 hour per day longer, then that cuts my free time per day in half. That is HUGE. You better pay me a lot for that.
With free college, more students from wider backgrounds could affort it. That would increase supply in college graduates while decreasing supply in workers of skilled trades. Thus, the latter would get to demand higher incomes (while the former would see theirs decreased).
And that does not even consider that my free time is very limited. If I have say 2h of completely free time everyday (24 hours minus work, commute, chores, gym, household crap, etc) and I need to work just 1 hour per day longer, then that cuts my free time per day in half. That is HUGE. You better pay me a lot for that.