Many US universities don't want to hire people who can't legally work at their location because applying for a work visa is tedious and risky. And in my experience, there are not many American academics working at British universities, let alone British academics working at American universities. And while the UK is definitely not Europe (universities are still dependent on tuition and tuition is high), it's certainly not the United States either; residents of Scotland don't pay tuition and UK student debt is treated very differently than American (for example, most of the students are never required to repay most of it). However, UK universities have no problem hiring strong candidates from Europe and the UK itself, for whom there are clear geographical advantages of living at most a short-haul family flight.
I was looking for teaching jobs, and most jobs in the UK publish the salary range and band, which (as I understand it) is essentially non-negotiable and adopted by most universities in the UK. Even for those who grew up in America, some may not find this as pleasant as the more distant and pervasive way of engaging with students that is the norm at UK universities. Universities in the UK tend to have a good pension match (20%), but this is also common in many US universities. American universities may also decide not to interview someone simply to avoid the cost of an international flight.
But from my experience with R1 universities in the United States, these advantages are really good, even for postdocs. There are many foreign professors in UK universities, perhaps even more than in the United States, so scholars who like exotic university social lives will have a really good time. The range of potential salaries in the United States is huge and prestigious universities will pay much more than less prestigious ones. It could happen that an academic wants to participate in the research work that is carried out in some university department in the UK and peer sympathy is worth more, at least for a few years, than the salary, since the research teeth are cut.
This means that if you can get a position at one of the best institutions in the United States, you will earn a much higher nominal salary compared to an average institution in the US. Compared to any university in the UK. The UK system is categorized into teachers, readers and full-time professors with significant salary differences between them, but a reader will have roughly the same salary across all UK universities. For many academics, the scale of US salaries and research budgets is a sufficient motivation for moving; if you look at the lists of professors of many American universities, you will find many surnames associated with China, Russia, European countries, etc.