Curiously, I hit exactly the same question with one of my children. We were in a hotel eating breakfast. He asked why this is called a hotel restaurant, rather than hotel's restaurant. It is a grammatical feature called apposition.

Curiously, I hit exactly the same question with one of my children. We were in a hotel eating breakfast. He asked why this was called a hotel restaurant, rather than hotel's restaurant. It is a grammatical feature called apposition.