I frequent a roundabout that bucks this rule, and it drives me nuts. Because the roundabout is part of a relatively major throughfare, people who are already in the circle need to yield to those who are entering from that one particular road. So as to not make the people on the major road slow down too much I guess?

It makes sense when you think about it, and It works OK if you’re familiar with the circle, but if you’ve never driven on it before and you miss the internal yield sign (or if you’re entering from the major road and don’t see the lack of yield sign), then you’re going to cause issues.