There is an obvious and common answer to this: college is expensive, both directly and in opportunity cost of not working. It's an expense that few people can easily afford without significant family support or loans.
Filtering by college degrees is filtering by family wealth more than anything else (or otherwise someone's willingness to get into debt).
I assume you have the US in mind? This is less true in the many developed countries where education is free and/or programs exist to cover living expenses during studies.
As an unrelated observation, the effect known as Berkson's Paradox would probably trigger along the way which is an interesting and little-discussed factor in this sort of thing. Two factors for getting in to college being wealth/connections and intelligence/ability.
Link for the lazy: https://en.wikipedia.org/wiki/Berkson%27s_paradox
As a counterexample: Dutch universities can’t select for students (for most studies), and annual fees are ~€2k annually (regulated). There will be some bias towards wealthier backgrounds that are more able to invest that money and time, but compared to the US/UK systems I expect it is minimal.
This is not unique, I think systems in the Nordics and Germany similar.
Wealthy students get the best grades since their parents send them to expensive schools designed to maximise this system. They then get into the "best" universities.
What do the Dutch do if there are 10k spots available in a given university and 20k people apply?
I didn't know that the Dutch had unlimited money. Weird that the portion of the population with degrees (44%) is comparable to the US (46%).
Exceptions happen: eg the popularity of CSI lead to a huge boom in people wanting to study forensic sciences. IIRC they were allowed to limit the seats for those studies back in the day.
Similarly, dentistry and doctors have a fixed amount of seats. They have a lottery that is biased based on your high school grades.
Overall I think this system has the better outcomes ‘on average’, but that the true top students are not challenged as much as they would be in a more selective system such as the US/UK
Yet, people who need to cover their own living expenses have a far smaller success rate, need to drop out more often or need to pause studies to work.
Programs to cover these living expenses exist, but they are limited, and not everyone who is not eligible for these can easily cover all expenses.
When access to education is considered an actual right, living expenses tend to be included in the conversation (as you just pointed out). Unlike merely incidentally affordable education.
My family could afford neither, and I don’t know what I would do if it weren’t possible to work in my favorite field without a god forsaken degree.
I'm not sure it's wealth as much as filtering by situation. My family was not and still isn't wealthy. Quite the opposite in fact. I was fortunate enough to be born near a local college so I could live with my parents while going to school, and working 30 or so hours/week to pay tuition.
I definitely didn't have the 'college experience', but I graduated with almost no debt.
I got my first programming job when I was a sophomore in college through people I met there. A couple different companies asked me to put college on hold for a semester in order to work more, but I'm glad I said no. College is not the only path, especially today. But, it was the best path for me.