Median pay for a dev in London is about £60-65k(a out $87,000). This isn't that high given the cost of living in the city, with your average shared flat with a few roommates going at about £1k a month nowadays. Add in that you'll be hitting the marginal tax rate of 40% plus 9% student loan tax and about 8% national insurance (ok income under 4k a month) and you don't end up with that much to live on.

The average university grad would be better off in law/finance/medicine by income in London. This isn't to stay the top software Devs don't get paid a lot, but it's a minority compared to the legions of high paid people in finance in London and the surrounding industries.

This is the very very small minority.

Jobs in London pay less than peanuts and if you earn six figures in the UK, income tax takes half of it anyway even if you go to FAANG.