The UK has 3 of the top 10 universities in the world: https://www.timeshighereducation.com/world-university-rankin...
It's a talent pool that many big employers want to tap into across a range of skills and industries. Cambridge is the best place to do bio-science and research. That is largely because the UK provides training and opportunities to its young people.
"I saw that 20 years go" is one data point that ignores the wider statistics. I'm not sure what else you can back your argument with.
The people who aren't graduates of those universities also matter.
These rankings are meaningless. If you actually studied in the UK, you'd notice a massive change in the last 5 years. Universities do not teach anymore (perhaps with a few exceptions), they are facilitating visas for foreign students without any expectation they'll be learning anything and nobody cares. They pass the exams barely attending any lectures. Everyone is happy, except home students who get massive debt and no actual useful skills.
That's rather the point: the UK has been great at educating a very narrow sliver of its population, decided at 18 years old. Pointing to Oxbridge as a success story is very much like pointing to London as a world city. Yes, it's world class -- now look at the rest of the country.