It's a bit of a confusing situation, but here's why:
* Bathroom: In America, "bathroom" is the common term for a room in a house that contains a toilet, sink, and often a bathtub or shower. This is the most widely used and understood term.
* Toilet: The toilet itself is called a "toilet".
* Restroom: "Restroom" is another term for a room with a toilet, often used in public places like restaurants and businesses.
* Washroom: "Washroom" is also used sometimes, especially in Canada, and it generally refers to a room with a sink and toilet.
So, Americans don't actually call the toilet a "bathroom". It's the room that's called a bathroom, and the toilet is just one of the things in that room.