

Sure, but you need to pay, and if all you have is a card, they’re not going to let you into an employee area because you’re being weird about a very basic interaction. In fact, that’s even more reason to not allow you into an employee area for their safety. When you’re in another country, you have to go with their flow, regardless of what you do at home.
Some places like diners and cafes do and you pay there with a cashier. But most bars and sit down restaurants have it inaccessible. As to why, I couldn’t say for sure, but I imagine it is to prevent theft of cash.