Why don't people just explain it with actual computers instead of pizza? MBAs are not that dumb.
People use mental models and heuristics and metaphors to make sense of all sorts of things. Very smart people do this, too.
Simplified maps can have their uses, even when you might personally be comfortable with a more complicated one.
Pizza is both tasty and fun - relating complex "serious" dry and boring work stuff to something else is a time-honored teaching technique.
I honestly didn't get it until an actual IT architect explained it to me with real-life IT example. (I'm a SW programmer, not MBA btw).