Clearly it's for the cavemen among us.

It goes further back than that .... it's at the moment some nutjob in the desert told a bunch of goat herders that he had a mental breakdown from hunger or eating some wild psychedelic and saw angels, demons and god in the wilderness ... and everyone just ran with it for 3,000 years as some sort of moral revelation that we all need to follow or else we will burn in hell forever.

sticks straw into the box hole and slurps up pizza

'It seemed to me,' said Wonko the Sane, 'that any civilization that had so far lost its head as to need to include a set of detailed instructions for use in a package of toothpicks, was no longer a civilization in which I could live and stay sane.'

Last time I visited the states I was dumbfounded to see a package of bagels with the warning 'remove bagels from plastic bag before placing them in the toaster'.

obviously someone ate the pizza first and then opened the box, that's why

https://en.wiktionary.org/wiki/joke

Sometimes on products I buy you see things like "don't put the plastic bag over your head" or "don't leave unattended around children". I always ask myself who that's for and then I remember the USA exist. :)

Edit: Also, we have a proverb here about this exact kind of warning. It goes something like this: "This is an American-grade warning, like not to put your dog into the microwave."

The Big Filter

Allergy warnings on products that are very clearly are made of potential allergens, such as a peanut allergen warning on a jar of peanut butter.

Tell it to my tummy, box.

C'mon as a child I didn't know I shouldn't swallow silica gel or put a nylon bag over my head, I learned those from reading the warnings or my parents telling me what they read.

Regulation

On a chainsaw:

Do not attempt to stop chain with hands.

WikiHow: How to walk

It's said that every sign exists because multiple people were too stupid for it to remain absent.

So exactly how many people tried to eat the pizza without opening the box first?

Or the one that says remove pizza from box before reheating