To many casual skiers, I think "blue square" = "it's a groomer." I don't think most casual skiers check the grooming report in the morning. So if they get on a bumped blue, they are going to complain. And if they get injured while doing that bumped blue... I think this is why everything blue tends to get groomed. Everyone else is doing it.
I'm not sure what the solution is. Maybe better signage? Maybe a new category of slope? Like blue triangle means it's blue steep, but it may not always be groomed. Blue square means it is recently groomed (unless it's a powder day). Black diamonds can either be groomed or not - I think that's understood by anyone who skis them. And someone who is familiar with blacks is probably also checking the grooming report.
Frankly, I find many bumped blue runs to be harder than bumped black runs. Seems the bumps get way bigger, icier, and have much weirder shapes on the blues vs blacks. Edit** So I think this in a nutshell is why the blues get groomed more often than not. Ungroomed, they can be worse than a black and piss off the most lucrative clientele.