When pharmaceutical companies are deciding where to direct their R. & D. money, they naturally assess the potential market for a drug candidate. That means that they have an incentive to target diseases that affect wealthier people (above all, people in the developed world), who can afford to pay a lot. They have an incentive to make drugs that many people will take. And they have an incentive to make drugs that people will take regularly for a long time—drugs like statins.
Diseases that mostly affect poor people in poor countries aren’t a research priority, because it’s unlikely that those markets will ever provide a decent return. So diseases like malaria and tuberculosis, which together kill two million people a year, have received less attention from pharmaceutical companies than high cholesterol.