They're responding rationally to a fucked up employment market that erroneously views education as an employee production pipeline.
If those perverse incentives disappeared, we'd see students more able to study what they want, not what's marketable on a resume.
If the perverse incentives of employers demanding significant amounts of ultimately meaningless education, people wouldn't go to universities. They would just go directly into training for a job (which has been the human norm up until a few decades ago).
Parents can view higher education as a social badge, and the students as something they have to go through, yet get valuable and life changing insights as they go through the courses.
Anecdotally the courses that were the most interesting and left an impression on me where auxiliary units we could choose from to fill a unit quota to graduate. The very low expectations kinda helped choose courses that didn't sound super useful, only to realize afterwards why they mattered.
I thought it was random luck, but looking at how the graduation system is set and the way the teachers organized these courses, it was obvious after the fact that the university put a lot of effort into getting students to touch subjects they didn't understand as important.
But even students treat it as such. Many of the people I know went to get a degree because they believed "they had to", not because of an intrinsic desire to learn. And if all involved believe that it is about getting a qualification for some career, then that is what it will become.
>when higher education in the UK was fully-funded by the state the resulting degrees, regardless of the subject(s) studied, were far more valuable in the job market
Rarity is the actual important thing here. If a significant portion of students have some degree it will be inherently irrelevant. Education has been continually broadened, making it more and more irrelevant. In the past a university degree was an enormous signifier, now it is "expected" in the job market, even if irrelevant.