There isn't enough money in curing cancer, the money is in the treating it.
1) We do have cures for cancer, and they're actually quite effective in most cases. E.g. breast cancer survival rates have nearly tripled in the past 60 years.
2) We do know some ways to prevent various cancers, including "don't smoke cigarettes" and "minimize sun exposure" and so forth. There's plenty of money in nicotine gum and sunscreen.
3) Research has placed significant resources and high priority on cancer research since the 1970s.
4) "Cancer" is an incredibly complex family of diseases. It's not like smallpox or polio, where we can whip up a vaccine in a few weeks (or months or years).