The text of that question says:
I am a tutor for first year math majors at a European university. By "tutor," I mean that I have office hours that all math students can attend. I am paid by the university.
Now, this is not the case anymore. Exercises consist simply of paraphrasing the definitions, and almost all the students are struggling pretty hard on these very simple exercises. Typically, they think that solving Ax = 0 when A is a 3×3 matrix is too hard. They have very little intuition about what is going on, especially in algebra. When they ask me questions, I try to answer so they see a way of thinking that can be generalized. But sometimes they just look at me as if I was an alien.
This is very surprising because I cannot imagine doing a math major without knowing algebra or matrix multiplication. Since they're commonly taught in high school, one would naively expect college-level math majors to not only know them, but to know them well. Without them, one cannot start learning the "real stuff". The obvious path of action seems to be to deny the student admission - if not to the college then at least to the major - due to the prerequisites not being met. But in this case, the linked question would be moot because it doesn't arise in the first place. Why doesn't this happen?
The only answer I can think of is that the students pay money to study math and the colleges are happy to take that money - but that sounds very cynical.