Hmm, touché :)

I think a restaurant is different though because that is explicitly how it works (eat first then pay).

To take your comparison further, what would happen if you sat down in a grocery store and started consuming hundreds of dollars worth of food and drink? I think it would raise a lot of eyebrows, and the employees would probably confront you. So there is a difference.

Furthermore, in a restaurant you place an order and they serve you, and from a legal perspective (IANAL) there might be something about some sort of implicit contract that you will pay them. Whereas with a grocery store you are not allowed to remove the items from the store until you've paid for them. And I feel like consuming the items inside of the store is sort of analogous to removing them from the store.

When I was young, I avoided restaurants because of exactly this! Always preferred cafes/fast-food places where you pay first. It just didn't make logical sense to me. I've grown out of it now obviously... :P

Doesn’t make sense. Paying beforehand is customary at grocery stores, not at restaurants.

I've never had unpaid-for groceries in a restaurant.