Adventure games use a lot of dialogue. Characters are going to have to talk to one another and, unlike books or movies, game dialogue is non-linear and gets complicated quickly.
To see just how complicated it can get, I laid out the initial conversation between Guybrush Threepwood and Mancomb Seepgood in the Scumm Bar early on in The Secret of Monkey Island. This conversation is short enough to be manageable yet still has many of the advanced features of a complex interaction.
