For centuries, their lives have been the same. Mabel would bring up the sun, and all humans would enjoy it. Then Dipper would bring up the moon and instead everyone would shun it away, choosing to instead hide away until morning again. This was a pattern that they were familiar with. Was Dipper happy that everyone ignored his beautiful night? No, not at all. But he put up with it because he hated confrontations. Until he meets a certain demon helps him realize that he deserves just as much respect as anyone else.