In reality, a company will look at the cure and know that it will end the market in management. They will also understand that whoever brings the cure to market first will take the majority of the profits, and the other will just lose. A company will not refrain from selling a cure to protect the market share of its competitors.

Your idea only works if you believe there is a global conspiracy of businesses and scientists who all agree to embargo research into cures, and who are all willing to forgo any profits on the cure while also recognizing any scientist and company not in their conspiracy could wipe out their profits at any time.