This may shock you to hear, but: In different places, people do different things.
I'm not sure where they don't have plain pizza, but here in New York, being able to make a good cheese pizza is a badge of honor. You're right in observing that it's a very simple food, and that's why it's so incredibly easy to screw up (and evident when done wrong). A good cheese pie needs to have the right ratio of acidity-to-sweetness in the sauce. The crust should be pre-fermented as a dough in order to give the crust a slight, but not overpowering flavor. It also ought to be hand-stretched as thin as possible giving a satisfying crunch as you bite into the fresh bread atop which your pie sits. The cheese needs to be ever so slightly pungent, but also not incredibly sour as to overpower the delicate mix of flavors.
When done right, a cheese pizza tastes like the color yellow, if you get me.
Certainly by-the-slice is a more uniquely NY thing, but we're not just eating room temperature pizza. It gets thrown back in the 450 degree oven for three-to-five minutes. Just enough to make it crispy and delicious once more!