I mean China is really rich, runs lots of centralized R&D, and has an excellent research culture, why isn’t it developing cures for everything?
The US has enjoyed a high concentration of R&D talent and funding which has somewhat starved out the desire of the rest of the world to do similar research.
If you are China, for example, why spend the funds to R&D new drugs when you can pull the same research from NIH and FDA efforts of the US and produce those same drugs for cheap.
And that isn't to say China is the only nation doing this. India is pretty famous for doing the same thing.
The issue with these drugs is once the chemical structure is known and proven to work, it's (usually) relatively trivial to spin up manufacturing.
China puts in R&D on products that are hard to manufacture even if the "how" is well known. They do that because China is a country built on international trade. That's why they are a world leader in battery tech.
Boner pills? Sure, go nuts on patenting those. But HIV prevention? No, it's immoral to patent this.