Straight walls

Can anyone answer me why in this country there are so many new walls which are not straight?. I have visited plenty of apartments in which there is not a single wall which is vertical and no two walls that are parallel. In many of them you could not even hang a picture frame because of the curvature of the wall (the frame being flat you allways leave big gaps between the wall and frame). Come on, it is not that difficult, the technology is there since many years ago: the spirit level!. Or is it that builders in this country have not yet learned to use one? Framemakers have!