Food is capable of causing burns when ready to eat, unless you like your food freakishly cold. I would indeed expect a freshly cooked chicken nugget to cause burns upon prolonged contact, or it isn't hot enough.
One might suggest the expectation from a fast food restaurant that "fast" food is "fast" because it comes directly out of the oven and is still going to be at oven temperatures when received.
The problem is that these things are subjective, and, since these companies are not prepared to fulfill specific temperature requests and there is no culture of making them anyway, the companies have to go with what works for most people. Most people buying coffee from a McDonalds drive-through are going to stick it in a cupholder.
So normies who expect their food hot and have never had problems with it get the takeaway about our crazy whiny litigious etc. culture, while the minority of people who always like to assume corporations are to blame for things get to feel smug about that instead, and nobody at all notices that placing a generic one-size-fits-all order with a company that specializes in perfectly uniform food-like product out of a machine and expecting it to come at the temperature - or any other property - you specifically personally wanted is actually insane. We have the same problem with spice or saltiness or anything else - and those things can and do harm people, too - but those just don't feed the culture war, so you just grab a couple of those little salt packets and go on with your day.
ETA: By the way... there already was a warning on the coffee. That case didn't even actually invent coffee too hot warnings.