Why do Americans call it a bathroom half the time there isn't a bathtub in it?

Well, now, technically you do not need a bathtub to bathe. You can use the sink to bathe. In America we have a lot of different names for it, so I guess it all depends on what you choose to call it or what you were raised to call it. We also call it the restroom, the John, the can, the little girls room, or the little boys room. In many cultures they have more than one name for the same thing.