One factor is that you have to convince patients

One factor is that you have to convince patients to participate in the trial. A patient who has not developed MDR would be more likely to just sign up for the usual ART treatment, and his doctor would be even more likely to do that. How do you convince patients to try a non-approved drug like Leron in a trial? You find more desperate people, who have already had trouble with the usual drugs. Once you've had success with rescue therapy, you can offer it to less complicated patients earlier in the stages of treatment.

Several of us have had friends whom we tried to convince that Leron could work on their solid tumor cancers, back in the days of the basket trial and the mTNBC trial. Their doctors wouldn't sign off on it, or the friends themselves saw it as a wild goose chase. That was a mistake, of course, but we saw it happen, didn't we? You need to acquire cred through trials.