Thats why "we the people" need to have large part in developing new drugs and the care of people, this is nothing that can be left to the "market" in some hope that it will "work out".
[1] https://www.thebalance.com/who-funds-biomedical-research-266...
[2] https://other98.com/taxpayers-fund-pharma-research-developme...
Public universities can do some initial poking around, but are utterly incapable of actually developing a drug. They've tried and failed many times.
As long as there is no practically usable permanent cure, everyone has a stable source of revenue from chronic treatment solutions.
Once anyone develops one, the chronic treatment would become significantly less attractive (as you say), so revenue would become less predictable for all parties, including the party that developed the cure.
If you have a monopoly.