We know lots of degrees don't really enhance job prospects of its graduates
However, what is less clear is whether those same people would get those jobs as non-graduates.
So while you might compare 'non graduates' as a group with 'graduates from a particular course' as a group, and find no particular uplift in terms of salary, the question is whether those PARTICULAR non-graduates - ie those at the lower end of the A-level results spectrum - would ever enter those jobs at all if they had no degree.
Many jobs once considered 'non graduate' are being filled with graduates - yes, the latter don't get the pay uplift they might have expected from their degree BUT they may still get the job in preference to a non graduate.
I suppose what i am saying is that for those caught on the borderline - to level or not, then to university or not - there isn't an obvious high quality well-regarded alternative. If they progress onwards through education, yes a proportuion will drop out, but a proportion will go on to get mid-range A-levels and mid-range degrees (or better), and while that option exists (and no other obvious high-quality mass-entry national path presents itself) it will be a direction that many students will still pursue.
(DS, highly able, has chosen a post-18 direction that is statistically unlikely EVER to be financially worthwhile. Worth is not always measured in money.)