You’re thick as pudding.

A clean kitchen isn’t enough. If your burger was made of preground beef you can’t eat it medium. If ONE of the pieces of meat that was processed that day in the factory was contaminated all the resulting ground meat is also contaminated. That’s why you cook ground meat to well done.

If a restaurant wants to offer medium burgers, or steak tartare or some other form of undercooked ground beef, they have to grind it themselves, in small batches, and use practices that reduce contamination. They’ll usually still warn you on the menu because there is still a risk. There are restaurants in Japan that serve raw chicken sushi, same concept. If you ask for undercooked chicken at a restaurant, you’re an idiot, unless you’ve gone somewhere that can do it right, which usually starts from raising their own specially vaccinated chickens.

Restaurants that don’t offer undercooked ground beef are just trying to warn you that you’re being an idiot ordering undercooked ground beef. If you make burgers at home from store bought ground beef and cook them to medium, same thing.