US corporate working culture is rather different to here. Here, if you don't take 4+ weeks holiday, your manager will have a word with you for working too much. Complaining about being back at work after a holiday is expected. At the end of the day, you log off and go home, and you don't think about work again until the next morning except in exceptional cases. Everyone knows and accepts that work is work, not the point of your life. 3PM Friday drinks is still a part of the culture in many companies, as is knocking off early on a nice day and going to the pub.
Obviously it's not like this in every job (particularly low salary or menial), but every job I and most of my acquaintances have had has been vaguely like this.
Then of course there's safety, environment, toxic politics, healthcare, etc. plus generally just liking what you're familiar with. I love the USA, but there are things that are hard to get used to, like car-only suburbs, jaywalking laws, beaches that close at night or are privately owned, rules against outdoor drinking...
I also find UK tech has less of an ageism problem than the USA. People sometimes return here after they start to find their age is causing problems finding work in the US.