That premise, of course, is true for many diseases. If they were cured, advocacy groups, various charities, pharmaceuticals, lawyers and others who make their living off disease in one way or another would all be out of jobs and millions in donations. It's a powerful conflict of interest, isn't it.
First, even if cancer is cured, people are still going to get sick...and, unless I'm mistaken, everyone's going to die eventually. Sometimes the level of cynicism is even too much for me to take...and I'm pretty cynical.
But I don't have a tin foil hat.