D&D rules are mostly combat rules. If somebody says they want to play D&D, most people assume they want to play in such a way that the D&D rules are relevant. This isn't a safe assumption, because the name "Dungeons and Dragons" is famous enough that some people will claim they want to play it without knowing what it involves. DMs should clarify to new players that D&D is heavily combat focused, and point out more suitable systems if the player isn't interested in that.