This is a self-fulfilling prophecy. People don't know how to use them because they never encounter them. Once they've been around for a while, people will encounter them and learn how to use them.
There are lots of roundabouts in the Boston area (where we call them rotaries). People encounter them regularly and STILL don't know how to use them. Although recently there have been great strides made in using lane markings to steer drivers through more effectively.
If Americans can put down their mobile phones and concentrate on the driving.