I believe we drive on the correct side of the road to allow our loved ones to alight onto the pavement rather than into oncoming traffic.
And so only the driver has to alight in oncoming traffic.
I'm convinced that the Brits developed the roundabout in an effort to get even with visiting Yanks for having lost the Colonies as a result of the Revolutionary War. And the bad part is, some obviously left-brained American transportation engineers have reached the conclusion that they're a good idea in this country.