There's an international co-ordination problem there. National governments don't want to foot the bill for research that the whole world needs.

So instead nations still foot the bill for research. The draconian US patent system proportedly produces more drug R&D than elsewhere, but where are those patents applicable?

The US, and anyone agreeing to honor its patents.

Everyone else gets free drug R&D without anything close to international discourse on funding drug research, because its privatized and thus in the scope of trade law.

Even better, the drug patent system means novel treatments are being developed for life threatening conditions that the suffers are disproportionately unlikely to be able to afford ("The Sick", as a demographic, are much poorer than average for obvious reasons). So not only are you subsidizing global drug research, you are doing it on the backs of the poor.

You can make an international body (or use the WHO) to fund such clinical trials then. It's not like we lack global organizations either.

UN budget around 5.5bn$ for two years, WHO around 4bn$. Not enough by a long way if drugs are costing 1-2bn$ to develop.

That kind of command and control economy was tried in many countries (the whole Soviet block) and pretty much failed spectacularly every single time.