Personally speaking (and I say this as a Brit who really likes the US, and Americans in general whenever I meet them). I haven't tried to move to the US because of the slightly distasteful situation in terms of education, healthcare and social security, car dependence, weirdly low holiday allowance, Foxnews, QAnon, an alarming gun lobby, and the current republican party in general is quite quite shocking to me in it's transparent gaslighting, racism and anti-democratic (small d) tendencies. The UK has its fair share of opportunistic charlatans too of course, ahem. That's why I now live in mainland Europe, get great health care, fast trains, fast internet, good work life balance etc though I probably earn less than I would if I was in the US
There are plenty of good reasons to move [to the US] too of course, and I do know quite a few who have (including my sister who loves it, and I suspect is never going to move back to rainy Britain)
There might be another reason you don't see many brit developers in the US though, we probably just don't produce that many of them. I worked in London for 20 years and the typical dev team had less than 50% Brits in it even there. Looking at Hollywood we seem to produce a lot more actors that can do a passable American accent than developers.