I did wonder that, but they do it even at traffic lights at pedestrian crossings.
I think you are right regarding corner cutters as I've noticed so many now making no attempt to turn properly and using both sides of the road at a junction. Mind you, I've also noticed that if I am at a T Junction on minor road waiting to turn right, more cars coming from my left ( on main road) stop and waive me out ...so they can then cut the corner as I am positioned so they can't cut corner
Yes, I now pointedly ignore the drivers letting me out, so that they have to take the corner properly.