You can extend this idea even further and ask yourself why pharmaceuticals never put serious work into full cures and permanent vaccines. An economist can easily answer the question: there's no long-term return on a one-and-done. That's why it's always treatment regimens and short-term vaccines where there's always a need for a return trip, guaranteeing one of those economic paradises: a captive market which guarantees repeat business. The only way to break this cycle is to seek an entity that isn't in it for money. About the only type of entity with both enough power and an ability to detach from a money motive is a state.