The problem with hydroxychloroquine is that it's not a magic cure-all, and it comes with very significant risks. For one thing, there's a very narrow safety margin before patients would suffer cardiotoxicity, and the high dosages required for HCQ to be even a bit effective against Covid19 is very close to that safety margin. Also, results are not consistent. For every report of promising results, like the case you mentioned, there are cases like this woman in NY who was given the same combination of drugs (HGQ + azithromycin) who suffered a fatal heart attack. There was also this study involving 81 patients that had to be stopped because the patients were experiencing dangerous arrhythmia. Other cases also report no change after HCQ treatment, while others suggest the treatment is only effective if given in the early stages of Covid19. There's no consistency, that's why you don't see any medical agency touting HCQ as a cure. They do suggest it as a
possible treatment, but since it seems to affect people differently on a case to case basis, they can't yet call it a cure.
By the way, there are other possible treatment options other that HCQ being investigated, including one you may have heard of: Remdesivir. But like HCQ, the results aren't consistent, but there have been promising cases. Another one I've read recently suggest that laying patients on their stomach (instead of face-up) may help increase chances of recovery. Which makes sense, since it eases the pressure on the lungs.
Anyway, since this disease is new, every kind of treatment at this stage is experimental. There unfortunately just hasn't been enough time to get a proper study done. It's perhaps fortunate that we haven't yet hit the peak while other countries already have, so we may benefit from all the lessons that the others have learned the hard way. It's a bit of a silver lining.