I agree with your last statement, and I'd argue as well that if you had the cure to say, cancer, you could charge whatever you wanted for it (at least in the short term). When it comes to money, you just can't take it with you, and you'll spend pretty seriously to improve your lifespan.
Fundamentally companies have to follow the science. If the science is there for cures, that is what is pursued. If the science is on life extending treatment, that's what gets followed up. You don't get to pick and choose what you want - both can be lucrative, and both can be failures!
Take diabetes for example. By the time a Type I diabetic is diagnosed as diabetic, they've lost a huge portion of their beta cells (something like 80% if I remember correctly). It is very hard to slow the destruction of those cells and harder to completely stop future islet mayhem. It's nearly impossible to regrow them with the information we have now. Even if it is possible to regrow those cells, can it be done by giving a drug, or a drug coctail? Maybe not. Maybe it has to be a stem cell treatment. Or an order of magnitude more difficult to discover: a stem cell treatment in conjunction with drug(s). Will that kind of therapy come out of a big pharma company? Maybe with partnerships with other companies or an acquisition, but the people who make small molecules probably don't know a whole lot about convincing stem cells to become beta cells; it's just a different set of skills.
I've also worked on 2-3 immunotherapies, they again can be amazing and turn previously uncurable cancer to long term survival (of duration unknown), but only in a fraction of patients - to work on them was an honour. Most therapies are incremental improvements, which can make a big difference to patients, but there is still unmet need.
GSK when I was there were explicit, half the drugs they wanted to develop internally, but using the commercial knowledge and experience guiding drugs though trial and approvals, also wanted half of drugs to be invented outside, and be commercialised by a company who knew how to do that!