Mrs. Duck at 2.42 has it right. Traffic lights are slower.

People who have never driven on a roundabout do seem to find them extra confusing, though. My wife was driving around one last year when the driver in front (gender and origin withheld) missed her exit, stopped, and reversed back past two exits! Fortunately, there was good visibility on the roundabout, and no accidents ensued.
The wife says it was fairly busy, but she had just been to her mindreading class.
I always wondered how come she was that step ahead!