They want to sell a vaccine, not a 4¢ per pill cure that takes about 5 days. If they can hold back the cure they think frantic, fearful people will line up for the vaccine. Govt will probabably foot the bill at $100/pp ≈ $32B (pure speculation by me on numbers). Then there is tanking the economy through delay of cure, social manipulation, possible additives in a vaccine ... and above all, an opportunity to make Trump look bad or something.