Alone in the apartment while Mama was out shopping with Kirsti, Annemarie and Ellen were sprawled on the living room floor playing with paper dolls

Why here used "on the living room" instead of "in the living room"?

Question

Alone in the apartment while Mama was out shopping with Kirsti, Annemarie and Ellen were sprawled on the living room floor playing with paper dolls

Why here used "on the living room" instead of "in the living room"?

Answer

They weren't just in the living room, they were on the floor of the living room.

Answer

Because "in the living room" and "in the living room", the former makes the whole sentence easier to read, but they all have the same meaning.