Because chronic diseases are difficult to cure? A solid portion, like diabetes, or cancer, are a whole host of different causes in a costume.

Anything that can be easily cured/trivially managed, or outright prevented isn’t considered a chronic disease any more. Beri-beri and Scurvy are non-issues today. Diabetes and AIDS aren’t the death sentences they used to be.

Medical research being deliberately gatekept because a cure would be unprofitable is conspiratorial thinking, and isn’t really reflective of reality.

A single dose cure for a chronic illness would be huge, and a lot of places would throw money at one if it existed, even if the cost was several orders of magnitude higher. No insurance, public health scheme, nor medical clinic would want a patient to take a constant course of medication, when they could have one, and be done. It’d be better for them, and patient quality of life. Even for the medication companies, they get to be in history books, and can get instant income, where a long term scheme might have patients dropping off for one reason or another.