Deadlifts do help you develop your hip muscles. The muscles targeted in the deadlift (or a few of them anyway) are the rectus, external obliques, internal obliques, and spinal erectors. The issue with deadlifts is that stress of doing deadlifts (the time under tension) is not enough to really help a person develop their hips (at least make them noticeably thicker). There are other movements that help one develop their hips (here are a few here).