Big pharma has been profiteering from peoples misery for decades. Big pharma doesn't create cures, just meds to ease symptoms so they have paying customers for life. Seriously, what hasn't aids been cured? Why do we still use radiation to treat cancer when it might kill or slow the cancer but also destroy your quality of life?
Well, I may not be a scientist but i can chime in a bit from what I know based upon what my Ex told me (She's a biologist)
She taught me that most diseases are fought off by your body's immune system, and drugs simply back it up in its fight. Whereas vaccines give your immune system a dummy version of the virus, i.e, a virus that cannot do any damage and gives your immune system a chance to learn what that invader is.
Since AIDS is a disease which directly attacks your immune system it's really hard to develop a "Cure" for it since whatever drugs they create for it can only suppress the virus's spread. Basically any cure would require a way to either directly target a protein that's specific to the virus (which constantly mutates so these proteins always change making an AIDS vaccine really difficult to isolate), or to figure out a way to drain all the blood and lymph from a person without killing them... Which is impossible. Most AIDS drugs are Retrovirals... Which are damned expensive in non-socialised healthcare systems (Like America's for example. Australia's got the power to talk them down at least a bit thanks to Medicare)
As for cancer, well... Cancer's essentially cells gone bad. Now like with viruses, the way that the Immune system deals with bad cells is to look at the shell of the cell to determine whether or not it's a cell worth keeping around. Now, there's a problem with Cancer. Cancer mutates with each cell it creates, so each cell is a little bit different from the cell next to it, and the initial cancer cell mutates because of some external or genetic factor. The human immune system's a bit stupid in that way. We like to think it's this really intelligent organism, but it's actually just a big dumb idiot that blindly attacks at the presence of a threat. Think of the Immune system more like an American drone pilot than Seal Team Six. It'll bomb anything that thinks it's a terrorist.
If it doesn't see that cancer's a threat? Well, it'll ignore it. Even if the cancer killing you, if the cancer can "trick" the body into thinking it's normal, it'll be left alone... So, when they administer chemo, Chemotherapy's a blunt force tool that kinda attacks cells that are cancer, and could be cancer. That's why you lose your hair and nails and stuff. Radiotherapy at least targets clusters of cells, but it has the very real potential of failing. Once again, the only way to isolate cancers is to isolate their causes and stop them in the first place.
Theoretically they've cured about 70% of ovarian cancers by isolating that those cancers were caused by strains of HPV. So, they came up with a vaccine for the strains which cause cancer. Bam, instant per-capita drop in Ovarian cancer rates. It's not necessarily "Finding a cure for cancer" but rather they're isolating cures for the things which cause individual cancers... Since there's so bloody many of them. But this once again comes down to the idea that without single-payer healthcare, Pharma can rip you off as you have a smaller customer base from a private insurer than a public insurer. That's why America's healthcare sucks.
Now this doesn't mean Big Pharma gets off scot free. No sir. The reason why they even can charge so much is entirely because America has an insurance-based healthcare system, and has a problem with rampant drug patenting making cheaper generics almost impossible for these more specialised drugs. This is something Bernie Sanders is trying to stop. Basically saying to the drug companies "**** you, it's about time you followed Australia's lead and make healthcare a human right."