Because American boomers treat them as 4 way stops and scream when they see a stream of cars zip by not giving them a turn. Their brains simply can't understand how they work. Too much lead paint and leaded gas eating their minds, I guess. My own Dad still swears up and down it's a 4 way stop and it's an hour long rant when two or more cars go buy "because of those damn circles!"
He'd never make it in Europe. Not a chance.