Many universities in the US are hesitant to hire people who cannot legally work in their location due to the tedious and risky process of applying for a work visa. This is why there are not many American academics working at British universities, and vice versa. The UK is not Europe, as universities are still dependent on tuition fees, which are quite high. However, residents of Scotland do not have to pay tuition fees, and student debt is treated differently than in the US.
Fortunately, there are now Profs online international business tutors available who can provide quality education without the need for a work visa. UK universities have no problem hiring strong candidates from Europe and the UK itself, as they have the geographical advantage of living close by. When looking for teaching jobs, most jobs in the UK publish the salary range and band, which is essentially non-negotiable and adopted by most universities in the UK. Even for those who grew up in America, they 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%), which 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. 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 US, so scholars who like exotic university social lives will have a great time. The range of potential salaries in the US 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 US, you will earn a much higher nominal salary compared to an average institution in the US. Compared to any university in the UK, the 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.