The truth is, many of us here in the Inland Northwest often act like rain rookies.
One way you can tell is that a lot of those using umbrellas seem to have utterly no idea how much space these weather shields take up. As a result, it is not unusual to have to do side-hops to avoid getting poked in the eye by bumbershoot-wielders making no attempt to share sidewalk space.
I don't think it's inconsideration. Not totally anyway. I think it is partly inexperience.