But I am more curious about culture as well. Pizza is very ubiquitous, and from my experience people prefer it even when they can easily choose something else to eat. Of course, many people just like pizza, but it is sort of a no-brainer to order pizza if team stays late, although it is simple to order something else.
edit: bad grammar :\
The history of pizza in the U.S. is itself fascinating. It was largely limited to Italian immigrants until WW2, when soldiers returning from the Italian campaign developed a taste for it. It exploded in popularity afterwards, particularly from the 1960s onwards. This is perhaps related to it being easy to eat without utensils, which made it convenient in the car/drive-in culture of that time period.
I was also surprised to learn that the vast majority of pizza varieties in the U.S. are actually American inventions, and that pizza in Italy basically consists of two varieties: marinara and margherita. All this stuff about pesto pizzas, BBQ chicken pizzas, meat lover's pizza, broccoli pizza, Hawaiian pizza, etc. are North American (including Canadian) inventions.