This would be a really good explanation as to why the blue wall is as pervasive as it is regardless of thr geographical location in US. I always wondered about

This would be a really good explanation as to why the blue wall is as pervasive as it is regardless of thr geographical location in US. I always wondered about and could not find a good reason ( after all, cities have their own PDs - you would think there would be maasive differences between them ).