'Cos most pizza places premeasure all their toppings pretty precisely; it's usually part of the prep. Actually, it's fairly common throughout the food industry; they watch food costs VERY closely to keep their overhead under control. Now, if you're paying them for four toppings and only getting one, yeah, you should scream to high heaven, but putting FOUR TIMES the "proper" amount of mushrooms on your pizza every time you call is a good way to get a pizza maker fired. Lessee, my job, your extra mushrooms; which is more important to me, let's ponder....

Sorry you keep getting disappointed though, but it's not that surprising.