Why is it that drinks but not food can have 0 calories?
Drinks are mostly water. If besides that it's just flavorings and artificial sweeteners, there's nothing with calories in it. So zero-calorie drinks are a really obvious thing to make: just take some existing drink, replace any sugar with artificial sweeteners, replace any actual food content (e.g. fruit puree) with flavorings, and it'll be zero calorie.

To make zero-calorie food, you'd need a solid edible zero-calorie thing to provide the bulk, and there's not an obvious choice for that, certainly not something common like water. On top of that, if you want it to be anything like the food it's based on, it has to be a very specific substance.

That said, it's not impossible. There are indigestible carbohydrates (fiber, generally), and some foods like shirataki noodles made basically completely out of that so they end up low- or zero-calorie.

I'm sure with enough modern industrial food science, we could make a lot more things in that vein. But it's definitely not nearly so easy as with drinks. And you wouldn't want to eat massive quantities; the water that makes up virtually all of a zero-calorie drink is easy to get out of your body, but giant amounts of indigestible solids won't be as pleasant.