My experience... the lanes are usually blocked because some other lane, coming some other direction, has much better access to those lanes because of how the signal timing works at the intersection.
A common scenario is: you're heading east, want to head north. When space opens up heading north, northbound traffic has a green light and fills it up. When you have a green light, there is no space.
I could imagine that left turns like you mentioned would be systematically disadvantaged, but doesn't that just mean you should circle around so that you are going north? If instead you were going west and competing against northbound traffic I find it hard to believe you would be systematically disadvantaged; a space is equally likely a priori to clear out when you have a green as when they have a green, no?
Space clears out when traffic upstream starts to move. If the next traffic light upstream is synced to the current one, then space will consistently open up at the same point in the cycle, favoring whichever direction has the green at that point. If the lights are almost but not quite synced, then the "favored direction" will gradually cycle around the intersection over time.
> circle around
This is generally not possible, especially for the kind of intersections that have this problem. There generally is not a short path that would allow you to circle around, and even if there is, it's guaranteed to be completely congested by everyone else trying the same trick.
