It's of paramount importance to know the answer to this question because billions of people the world over are MISSING OUT on a delicious dish.
Many professional chefs prescribe to the "sweet/salt/fat" flavor profile group in the dishes they create.
Pineapple is a sweet, acidic fruit that pairs surprisingly well with the sweet acidity of tomato sauce, the fat and salt of melting cheese, and the perfectly bland background of crust.
Critics will say that the classic existing sweet/salt/fat flavor of pizza should not be tampered with, but the same was said about changing the original Napolitan Margherita pizza to ANYTHING ELSE... so, by that reasoning, there should be NO toppings added to pizza, ever. You cannot have it both ways. Either toppings to the classic Margherita are acceptable, or they are not.