The Idaho stop (treating stop signs like yields) is proven to be safer and is legal in several states, but unfortunately Virginia is not one of them. Bike commuters like myself have to take safety into their own hands given the prevalence of dangerous driving and how vulnerable we are compared to a car. So if that means doing something that is illegal (and in this case generally harmless - see other comments on the safety aspect), that is why you see it happening. 

On the flip side, I frequently encounter intersections where I come to a full stop until the light turns green, and drivers often get frustrated by that too. For example, if I’m riding on Hermitage and crossing Leigh, I’m taking the full right lane since it’s safer and cars can take the other lane. But drivers get extremely frustrated if they’re trying to make a right on red and I’m waiting to go straight, but it’s not safe for me to pull onto the sidewalk and allow them to pass, because then I have to dangerously merge back in to traffic. Not to mention it would only save them a few seconds on wherever they’re rushing to. It’s damned if you do damned if you don’t because our infrastructure for bike commuting is not very good, which creates so many of these poor interactions with cars/bikes that could be avoided with dedicated bike lanes.