This is a long discussion. There are scientists and Nobel prize will come to them for finding a cure. It is always a life goal for them. You cannot deny this or you don't know what it is to be a scientist. On the other hand there is the company profit. They are merciless soulless coops. But they cannot control scientific discovery. They have to follow and compete each other. There are many parameters to consider than just suggest they "hide the cure that already exists"... I was never a big fan of such conspiracy theories.There's more profit to be made in a life long treatment course, than a cure in one month.
On the other hand, there is the question of time and stalling, that may be of importance here. There are scientific breakthroughs in hearing loss that are lost at the stage of finding a pharmaceutic companies to provide the means to put the discovery to practice, especially in humans. The latest example is that of the regeneration of the synaptic connections between hair cells and neurons (Gabriel Corfas, University of Michigan's Kresge Hearing Research Institute). Until their finding in October 2014, no more news can be found on the net! There is an interesting article here and nothing more. That may suggest nothing but things do move really slowly, if they move at all!