Isn't it illegal to pass in the middle of an intersection? I always thought it was, but I could be wrong. When I'm driving I never pass other cars in intersections because I believe it is dangerous. By passing in an intersection you're introducing another dynamic element into a situation that already has a number of other variables (including people turning, etc). In these wide intersections, motorists who pass are going way outside of the bounds of their lane in order to do so, which is quite dangerous also because it makes it unpredictable where they will end up on the other side.

The problem happens when the road is too narrow to share on the other side. Many times the side road will be too narrow to share, but the intersection on the main road will be huge and wide. So the cyclist needs to control the lane to prevent the pinch on the other side, but can't effectively do so because of all the cars trying to dangerously pass in the intersection (some of whom will attempt to pass at unpredictable or late moments). I agree that communicating with the drivers is key, but that often breaks down at some of these wide intersections with brief green cycles because the drivers get so impatient and road-ragey just from the traffic situation. They're more concerned with making sure they get through without having to wait for another cycle than with doing so safely.