Why do people in america say that ghost has been seen?

there are two reasons, one is because of cultural beliefs like he just sauid, but there are also entities that actually exists. things without reason like missing books, moved keys, and strange noises are simply a thought of ghosts. but these are simply because of people forgetting where they had put stuff, and people going crazy because of self-crazed thoughts, and hemerophillia disphixia

also known as the crazy or mentally insane.

It's a common misconseption that ghosts exist and due to pop culture we americans believe that they exist.