Not really true. A ultra-highly paid hedge fund manager or corporate lawyer will pay off their student loans very quickly so will incur much less interest. Whereas a more "middle" earner, say £50k per year, will be paying the student loan repayments for the full 30 years, and probably still won't have cleared it because of all the interest added over those years, yet will have still paid back far more than the amount originally "borrowed". The killer is the interest, not the capital amount borrowed. If it was either interest free or if interest rates were more reasonable/normal, then I'd agree with you that taking out the loan regardless would make sense, but with interest rates being so high, taking out full loans if you plan to be a middle income kind of earner doesn't make sense.
The thing is, someone on £50K isn't a "middle earner". They are a high earner. If people are training for something like Nursing, teaching, to be a police officer, a SaLT, a physio, an OT, a social worker, a librarian, etc etc etc they are never going to earn that, (unless a teacher moves to become a HT, which is a tiny fraction of the people who qualify for those roles). I am a senior manager in my (graduate) field, with over 30 years experience but I can't hope to get to £50k, let alone be earning that in any of the first 30 years since graduating. The pay just doesn't go up that high.
Then there are a lot of people who graduate now who are not even able to get "graduate roles" (by 'now' I mean over the last 15 - 20 years).
Then there are the people who work PT for some of those 30 years - parents, other carers, people who become ill or have an accident or mental health breakdown. People who are caring for parents or for people with SEND.
Then people who decide to branch out on their own / start a business / re-train later in life and won't be earning for the next 3 years, or earning a pittance.
It would be only a tiny minority of people at University now who will be earning £50k for 30 years, even those who qualify in professions where they can work up to that.
No other loan / mortgage allows you to just stop paying it when you don't earn enough. I'd rather have £30,000 less on a mortgage than £30,000 less on a student loan.