As others have said there are hundreds of types of cells, all of which can screw up in their own unique ways (likely many multiples thereof).
Going further the problem is not necessarily cancer itself but what it otherwise does to the body as part of it all. Judging by all the fat bastards in the world your body can survive well enough carting around a bit of extra mass (actually I wonder if the average mass of an average lethal tumour is less than that of having long hair), pumping some extra blood and looking at athletes and no athletes taking in a bit more oxygen.
However when that mass is located somewhere that starves something else of blood/energy/oxygen and in turn kills that or prevents it from doing what it needs to do then that is what tends to kill you. A cure would necessarily involve fixing that, and a cure like that would make no distinction between fixing a blood starved kidney from a tumour pressing on an input blood vessel, and an input blood vessel damaged by some trauma or something. I can not believe for a moment that the people sitting on such a cure would lack the imagination to want to commercialise that. Even if by some demented twist of chemistry it was the tumour itself that stored the chemicals/energy/whatever necessary it would in turn mean that a cancer would be induced to fuel the cure for another disease (to continue with the kidney theme ask anybody on dialysis if they would carry on business as usual for a month or three to then be completely cured).
More lucrative to treat than to cure? A few months of chemicals, all of which have to go through fairly extensive and expensive trials to last maybe a few years, and radiation vs a lifetime of other chemicals from my very same company that are well known and mass produced and theoretically other procedures? In the vaccinations thread I ran the numbers for treatment vs prevention, the conspiracy died on its arse before going anywhere. Do I have to do the same here? I had a quick look at costs of a course of chemotherapy and while it is not pocket change it is about in line with many other drugs per month.
If instead of cure you meant vaccination, or maybe some kind of ultra reliable and easy to deploy screening that could catch things before it ran amok, then it would run contrary to all I know of the matter. Admittedly that is not a huge amount but the overlap between than and sciences I do know is enough that if the cure almost any damage thing above would speak to a lack of imagination then the ability to turn around and detect trace indicators from a blob of goo would be so incredibly lucrative in everything really* that to not deploy it there is nigh unthinkable for any kind of money hungry types that would betray all ethics and somehow manage to silence all researchers on the matter.
*hands up anybody in the plastics, construction, clothing, water supply, wood, food, paint, makeup, semiconductor, banking (no mate I can't loan you this unless your cancer is sorted) or anything based on material goods field that would not want a trace contaminant test of that kind of accuracy, ease and reliability?