When you tip for takeout, who do anticipate is receiving that money? You didn't interact with a waiter, a maitre'd, a sommelier, and the owner didn't come by to ensure everything was good. The cook/chef (who is, realistically, the employee most worthy of receiving a tip) only gets a small slice of pooled tips. It's a bit absurd to tip for "service" when you received no service, and there's no employee to whom you're directing the tip. It's just like, hey, here's some extra money for whoever wants it...