Leg Brace after hip surgery, why do I have to wear it?

Hip replacements aren't usually followed by wearing a leg brace. Hip spica brace maybe in a few unusual cases where dislocation is a problem, but not leg braces. Must be something else going on. No one here can tell you anything about his leg.

You don't say which prescriptions he is not taking as prescribed. If it's pain meds, that is probably not a problem because that may mean he doesn't have much pain. However if it's a blood thinner that he is "forgetting" that's not such a good thing. They are prescribed for a time following hip replacement surgery to prevent the formation of DVT [blood clots in the leg] which can lead to the development of potentially fatal condition where clots from the deep leg veins break off and lodge in the lungs causing a pulmonary embolism. Very serious stuff.

Hip Brace After Surgery

I never heard of someone having a brace after hip replacement. Usually they are into physical therapy right away and moving it. This must have been more involved than normal hip replacement. Your friend needs to talk to his doctor about alternative treatments that are possible...