Because it's not just "higher" - it's so much higher it's hard to comprehend what difference that makes to opportunities young people have. I finished my BSc and MSc in Computer Science from a prestigious Russel Group university 10 years ago, got hired as a C++ programmer for a big corporation.....making £18k a year. My take home was about £1200/month if I remember correctly, which was still ok-ish because I was sharing a flat with some people so I only paid like £150/month towards the rent. I was only able to save a very modest amount of money and it took me years to work up to what you'd consider a "decent" salary.
From what I understand, in US your costs are of course higher in terms of rent, healthcare, etc, but the difference in salary is so huge you can actually save up some capital if you want to try starting your own business in few years time.
£18k/year as a junior programmer in London in 2014? I was underpaid as a junior at £16k/year in London (fintech) in 2004, and we were paying junior developers in the high twenties in 2015 in the public sector. You were definitely being seriously underpaid.
I was earning 35k in Nottingham as a C++ programmer with 3 years' experience in around... 2006 or so. Most of my programmer friends were in roughly the same pay scales. Programmer salaries in the UK aren't usually that low.
From what I understand, in US your costs are of course higher in terms of rent, healthcare, etc, but the difference in salary is so huge you can actually save up some capital if you want to try starting your own business in few years time.