Here’s a link to the Hydroxychloroquine dosage for diseases:
https://www.drugs.com/dosage/hydroxychloroquine.html
Please look at it; no need to read it in detail. All those protocols and warnings are developed from extensive scientific studies, not from one or two limited trials.
Please understand there is absolutely no government restriction on using hydroxychloroquine right now to help people who need it. It is already defined for usage on an empirical basis in a number of hospitals for treating coronavirus patients.
Studying drug usefulness for a new infectious agent is a good idea, but once you have a drug which has been FDA approved, as you note there is no reason not to use it against a new infectious agent. That is doubly so once you have some clinical test results showing it is effective in treating the new infectious agent.