The smell from just the store is enough to make you feel sick? Weird.
Just wait until you have to deliver...
The thing with all of those different kinds of toppings and feast combos on pizzas is... each different kind of pizza has its own funk, and in that small confined space of a car, it concentrates, blends, then penetrates every bit of fabric and nook and cranny in the car.
Sure, just a bunch of cheese pizzas would be fine... but ohhh nooooo, each person has to go and order something different.. and don't you doubt that they do this intentionally, just to stinkify the delivey vehicle!
So you get the blended perfume of... Barbecue sauce, Onions, Pepperoni, Peppers, Sausage, Mushrooms, Tomatoes, Chicken, Pinapple, Ham, Banana peppers, Anchovies, Black olives, Ground beef. All mixed with the heretofore lovely scent of Pizza sauce and cheese... and what were nice smells individually become a mass of monstrous olfactory overload.
Dont think that if you go for a drive on your day off in the same car, you'll be free of the smell... because you wont. It takes a good two weeks, no matter the amount of interior cleaning, for the smell to dissapate.
I suspect the cessation of the smell is only because the legions of bacteria have devoured every scent particle, after a week or so... and after farting out the gasses for another few days, they eventually croak, then decompose, releasing yet more gasses... or better yet, junior comes along and eats the dead bacteria parent, laden with pizza gases... so the cycle can continue. If ever you get that strange waft of pizza stink, and you will, a month or longer after the last pizza went anywhere near the car... rest assured it was only the great, great, great, grand-offspring bacteria, otherwise known as junior, farting its last gassy pizza fart.