It's a tempting conspiracy theory, but there are a few reasons that persuade me it's very unlikely.
1. Researchers build careers based on reputation. The reputational value of "cured cancer" (even for some small subset of cancer) is probably worth more than a lifetime of developing treatments.
2. Also, some motivated researchers have lost family or friends to the diseases they're working on.
3. Also, many researchers are simply not working at for-profit companies.
All of the above can be filed under "profit is not the only motive for curing diseases (even if it's a powerful one, it's not the exclusive one)." A different tack:
4. Many lines of research have unpredictable results. Studying a virus to develop a treatment may uncover a key weakness that results in a cure. Foundational research often is too early to prioritize a use, and breakthroughs happen in unpredictable ways.
5. There are a lot of players involved in research. A big mix of for-profit companies, NGOs, and governments might have to collude to avoid developing impending cures. So if there's an reasonable next step for global research, it'd be a bad gamble for a company to avoid it, hoping that no one else would pursue it either. ie, If you can get there, assume others can too, so just claim the credit.
EDIT: OTOH if you want to run with this line of thinking, there's a great classic comedy called "The Man in the White Suit" starring Alec Guinness. He invents an unstainable suit that never needs cleaned, and the garment industry sends people to stop him.
If nothing else, many academics are motivated by ego rather than money (I'd put myself in this category). Having successfully discovered a cure for HIV would do such spectacular things for my career that the level of money that would have to be involved is pretty substantial - and would have to be spread over a large number of people.
1. Researchers build careers based on reputation. The reputational value of "cured cancer" (even for some small subset of cancer) is probably worth more than a lifetime of developing treatments.
2. Also, some motivated researchers have lost family or friends to the diseases they're working on.
3. Also, many researchers are simply not working at for-profit companies.
All of the above can be filed under "profit is not the only motive for curing diseases (even if it's a powerful one, it's not the exclusive one)." A different tack:
4. Many lines of research have unpredictable results. Studying a virus to develop a treatment may uncover a key weakness that results in a cure. Foundational research often is too early to prioritize a use, and breakthroughs happen in unpredictable ways.
5. There are a lot of players involved in research. A big mix of for-profit companies, NGOs, and governments might have to collude to avoid developing impending cures. So if there's an reasonable next step for global research, it'd be a bad gamble for a company to avoid it, hoping that no one else would pursue it either. ie, If you can get there, assume others can too, so just claim the credit.
EDIT: OTOH if you want to run with this line of thinking, there's a great classic comedy called "The Man in the White Suit" starring Alec Guinness. He invents an unstainable suit that never needs cleaned, and the garment industry sends people to stop him.
https://en.wikipedia.org/wiki/The_Man_in_the_White_Suit