Why haven't we cured leprosy?

We have. Leprosy is curable for the individual patient. May be you mean, why have we not eliminated leprosy? If that is the question, the answers include lack of an effective vaccine and failure to eliminate poverty.
Agree w Dr. Singh. Per WHO- Leprosy in endemic in 91 countries. Over 50% of Leprosy in the world is centered in India. There are areas of high prevalence within Nepal, Burma, Brazil, Tanzania, Madagascar & Mozambique. Leprosy can be effectively treated with dapson, rifampicin or clofazimine. However, Lepers remain outcasts & often there little to no $.