Some recent research seems to indicate that caries producing bacteria may stimulate the immune system in a way that reduces the risk of oral and neck cancers - http://www.nlm.nih.gov/medlineplus/news/fullstory_140610.html Things are never quite as simple as we may like.
I take a daily antivirus to control hepatitis B. I’d love a course of treatment that meant I didn’t have to do that every day. I had to make the availability of ongoing similar treatment a priority when I started planning my return to NZ from the UK. I could not plan to live in the US, as the cost of the drug would be prohibitive - up to $1000s per month. I don’t even know about Australia. It restricts my choices and I have to be on the ball every day. But I also know that the drug was hard to develop, expensive to test, and that costs in the west actually do subsidise the $1 a day version used to treat HIV in Africa. I am also aware that finding and eliminating a virus that hides in my own cells is hard. But we find new clues all the time - new genetic studies may have found the protein that some people miss that allows the herpes simplex virus to hide in nerve cells and reactivate. A new pathway to explore, new possibilities for that and other viruses to be treated in a new way.
Finally, I have a friend who is a chemistry lecturer at a UK university - he works for pharmaceutical companies, synthesising and modifying bioactive chemicals to improve them as treatments - generally changing the pharmokinetics by adding new groups and atoms. It is hard, painstaking work, and most attempts don’t provide the desired benefits. But he likes the fact that he and his students help people in the long run - someone might make money (not the chemists, I might add, they just get funding), but there is a general benefit to humanity when they develop a better treatment or eliminate a poor one.
I think a counter-balancing factor is you’re not just selling the cure. You’re selling the whole medical care package. Cures for disease are basically just the final pay-off. You’re also selling the course of examination and diagnosis that identifies the condition and leads up to the administering of the cure.
Without an effective cure, there’s a lot less market for the examination and diagnosis. You have to have a cure for a disease on hand to sell people on the idea of finding out if they have a disease.
Pharmaceutical companies are not in the business of selling a whole medical care package - they generally do not get into the diagnosis business (although that may be changing somewhat as genetic factors come into the equation as a way of identifying which drugs may be best for a patient). And there are plenty of diagnostic procedures in development and use that do not have a cure - knowing what you have and what will happen is important even if there is no effective treatment. I’d rather know I had progressive terminal disease even if there was no cure.
Knowing how to identify a disease may give clues on how to treat it, but the two are not linked in any profitable way for pharmaceutical companies.