You seem to have a very ill-informed view of UK/EU salaries in this particular sector; And also: yeah, people take salary hits to go do things they believe in (this is like, the entire premise of the underpaid American startup founder model) - it should come as no surprise that people are willing to forgo pay for reasons other than just building their own business / making themselves personally wealthy.

We're talking about the "brightest scientist and engineers" in the AI sector, you may be underestimating US salaries for the people that's referring to.

And no, working remotely for US companies doesn't count.