There is also the other aspect that many able pupils aren't attracted to the "top" unis like Oxbridge, StAndrews etc.
My son went to a top 50 state grammar school. Looking at leaver destinations over the last few years, they only had a handful going to Oxbridge, despite a cohort of 300.
The school, teachers, sixth form tutors, etc., were all heavily pushing the students to apply for the "top" unis, even organising & financing visits, etc. My son was positively harrassed into going on one of the trips to Oxford. It turned him right off. He was forecast 4 A* (which he achieved), so had the choice, like lots of his friends. But they've mostly gone to a wide range of Unis. My son finally chose a non RG uni which his sixth form tutor gave him lots of stick for putting on his UCAS application, but he loved the place at open days, loved the ethos, loved the location, loved the course (very relevant to modern working life), and it's still a Top 10 despite not being RG.
He went to lots of open days at the "top" unis, including Durham, St Andrews, LSE, etc., but just didn't get good vibes.
I'm not sure it's a good thing to constantly look at Oxbridge at the Gold standard. There are dozens of excellent universities, many of whom have a more modern outlook in terms of subject choice, university life, etc, many of whom rank higher than Oxbridge in league tables etc in certain areas. For a lot of students, especially who come from a non Uni family background, Oxbridge is a step too far.