Because this drug can be cheaply manufactured out of patent. Let's say Remdesivir is the only drug that works, it's basically an admission that Gilead is going to have us over a barrel.
That's absolutely not what would happen. I was chatting with a family member who used to work in biotech/pharma and posed the question what would happen if Remdesivir is found to have efficacy against covid-19. What they said is basically there would be licensing done immediately to other pharma companies which would run manufacturing in parallel with what Gilead is doing. Gilead will be getting profits from each pharma company that gets a license. I am unsure why the lead time is so long, however it may be that the company does not want to create a huge supply of a drug that may not be effective. But this is very interesting, the pentagon is getting lots of remdesivir for troops so there must be some info that leadership has about its success rate: https://qz.com/1834939/how-the-military-secured-experimental...
The US government could simply seize the patent if Gilead acted in a manner against the public good.
Incentivizing people to not do productive things like develop drugs seems like a really bad idea.
[1] https://ccbjournal.com/articles/benchmark-metrics-pharma-com... [2] https://www.investopedia.com/ask/answers/060115/how-much-dru...