It kinda is though. Iirc it received an interrupt it shouldn’t have received and doesn’t know how to resolve. It is not supposed to ignore it, but then the only other option is crashing at this point. Basically it continues in a dazed and confused state.
Of course the message could be clearer, but at least it also makes the message easily searchable.
I think mixing horizontal and vertical is impractical, because it will mess up the whole layout once you resize a single window, but on one axis the concept is actually sound. There exists PaperWM for gnome 3 which is basically just this.