Because American drivers have a sense of entitlement that precludes them having to obey yield signs, believing that their excursion out is vastly more important than yours, allowing them to blast through without slowing or stopping and then getting butt-hurt when you honk your horn at them.
About 1.5 miles from my house are three roundabouts within 400m like an infectious disease.
Welcome to Noosa, Queensland. And, Canberra, and Milton Keynes.
There's always this one!
https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)
I believe if you drive round it 7 times playing the trumpet Swindon Town hall falls down.
Because American drivers have a sense of entitlement that precludes them having to obey yield signs, believing that their excursion out is vastly more important than yours, allowing them to blast through without slowing or stopping and then getting butt-hurt when you honk your horn at them.