If by “cold overnight” you mean unrefrigerated, I doubt that anything like 1/3 are.
https://www.fda.gov/food/consumers/what-you-need-know-about-...
If anything, there should be more lawsuits against companies and they should be punished punitively.
I'm going to guess this is wrong. I went to a large private university of around thirty thousand. I'd estimate, on any given week, the average student has eaten leftover pizza in the morning once. This alone puts us at a hundred and twenty thousand overnight pizzas consumed per month. Millions per year. At just one university! Surely we'd hear cautionary tales of overnight pizza at 1 in 100k or even 1 in a million, as deaths from it would be far more common than binge drinking.
My estimates may be off a bit, but probably not by as much as you'd think. Student organizations buy copious amounts of pizza because it's popular and cheap.
Advice to huge numbers of people skews the odds of "this is probably fine", which I think is the root of this. Aside from the fact that quantifying just how many zeros are in front of that probability hasn't (can't?) be done. It probably _is_ reasonable to estimate based on prior science that if 300,000,000 people leave pizza out a few times a year, there's a one in a billion chance of warm cheese making someone super sick.
I also wonder how much lawsuit culture plays a part in this, it only takes one bad luck case.