It's hard not to be incredibly cynical in the face of things like this. Way more than once have I thought "this is a cruel and unusual punishment" -- wait aren't those prohibited?? Oh right we get around that by making cruelty usual.
The number of doctors and nurses that attempt to keep people chronically ill rather than curing them if possible, is essentially zero. People get into that field frequently because they actually care, and people that actually care are the most likely to not follow a vague profit incentive that actively hurts people.
Similarly, most medical researchers would love to cure diseases, and actively seek out jobs where they do so and will object if asked to suppress curative research.
To the extent that what you describe exists, it is limited to MBA people at insurance companies and big pharma determining what gets funded for research. While exceptions always exist, the incidence of that attitude among the people actually doing the work is very close to nil.
Sorry to annoy you.
A healthy person is a huge asset to an insurance company. Collect premiums for decades before they need much of any disbursal! They're still likely to be expensive at end-of-life, but you've profited WAY more from their initial healthy years.
(This, of course, is why insurance companies want to consider health in setting premiums, and why it's SO IMPORTANT that the government not allow that and keep things group-based. Because then you have the incentive to help the unhealthy people instead of just "milking the unhealthy people.* I pay the same as my coworker for my insurance. The insurance does NOT want my chronic condition to make me much more expensive to them than my coworker. They'd much rather it go away. Sadly, nobody can do that today.)
What the insurance companies don't* have is the incentive to actually push doctors and facilities to spend more time and money on looking for rare issues for unhealthy people. Because the searching is expensive, and there's a high risk it won't actually find a magic bullet.
So they'd rather have the median patient go from unhealthy to healthy, but if we want them to invest more in the long tail, it's gonna have to come from regulation.
And targeted investment in better detection*. But better detection is harder to sell than "expensive treatment drug" so again. Might need to get the state involved.
I'll grant you that that is a low percentage of the total US medical research spend. But also, most of the world does not have the same profit motive; in most Western countries, a cure is categorically cheaper for everyone than a chronic illness, because healthcare is paid for by taxpayers. And countries besides the US do plenty of medical research.
If the hypothesis were true that there exist cures to many diseases that simply haven't been explored due to profit motive, then I would expect countries without that profit motive to have a higher proportion of cures among their medical.discoveries than the US. I don't believe that is true though.
Basically my point is that the effect you mention likely has little actual impact on the larger medical field.
That's not actually a thing. A very high portion of premiums always has to be paid out. Not just because the regulators said so (IIRC the requirement is a 90% or 95% loss ratio?), but because they'd be undercut by a competitor long before they got in regulatory trouble.
People want a pill to solve the ailments they have.
If you have high cholesterol and you decide to make lifestyle changes, you still have to go to the cardiologist. Because you have absolutely no idea if you actually lowered your cholesterol.
A big fallacy is people thinking they know if they are healthy or they know about their bodies. You don't. Even if you live a very healthy lifestyle, you still have to go to the doctor. You still need screening.
Most chronic diseases are primarily caused by lifestyle choices. This is largely outside the scope of medical practice. A doctor can prescribe metformin to treat type-2 diabetes and a statin to reduce cholesterol but they can't force you to clean up your diet and get some exercise.