You are mistaken.
Mostly because we know the cause of HIV. We can identify and "see" the virus and its properties. We have almost no information about the cause of cancer - only numerous plausible theories.
Cancer treatments have improved hugely in that time. 30 years ago pretty much anyone who got a form of cancer died. That is absolutely not the case now. But also you are comparing two different things; HIV is one virus but cancer is a whole family of disease, each one of which is unique to some extent and requires specifically tailored treatment.
There's a lot more money in NOT curing cancer.
There is one cause of HIV, and we know what it is.
There are multiple causes of cancer, and we don't know most of them.
Some would posit that the treatment of cancer is far more profitable than the cure for cancer
Single illness v. Many. Cancers are like colds. It's not one single virus.
Lots of money to be made in cancer research and treatment. Don't expect to ever have a cure, they gravy train would be lost.
Andrew is right that cancer has many causes. It's the normal splitting and creation of new cells, gone wild. But you're wrong that treatments for cancer haven't improved. There are now much better treatments, including ones that target genetically caused cancers. St. Jude has a huge success rate in curing childhood cancers now. Targeted approaches are curing people without massive surgeries.
Actually, cancer treatments HAVE improved enormously over the last 30 years. People are surviving cancers, or at least living longer with them, that would have killed them a few decades ago.
One great advance is the ability to genetically test for and identify different strains of cancer and tailor treatments to them. That's been hugely important.
But because there are so many different types of cancer, the treatment situation has always been very, very different from that involved with HIV.
What makes you think they haven't?
Hodgkin's lymphoma is almost 100% curable. Metastatic melanoma had a 5-year mortality rate of 85% just 15 years ago. That has completely reversed in just the last ten years.
I could keep going.
That you don't HEAR about those advancements doesn't mean they aren't occurring. It means you're not paying attention to the right sources of information. Cancer treatment has progressed tremendously in the last ten years. Several cancers that used to be fatal are now treatable and even curable. Plenty of others are like melanoma -- it is still a lethal cancer but the survival rates have jumped an order of magnitude. Immune therapy and targeted genetic therapy are changing both testing and treatment very quickly.