It makes total sense to focus on moderate to severely ill patients, rather than people who aren't very sick. Many people get "mild" cases (which are still really bad) but some people really do get infected and are contagious but not symptomatic. We don't know enough yet about this disease to know why some get a little sick, or not sick at all, and people with a similar demographic profile end up in the ICU. The genetic testing is looking promising.

So, it makes sense to study people who are quite sick (a "moderate" case means you are really, really sick), or so sick that they are on a ventilator or the supplemental oxygen that they are learning how to use instead of ventilators. You can get measurable results by the most basic of measures -- how long till they recover, on average, do moderate patients progress to needing the ICU, and do the critically ill patients recover at a higher rate than the non-Brilacidin group?

Trying to do a study with people who aren't extremely sick would be difficult to measure success. With much sicker people, it's lots easier to see if Brilacidin reduces the length and severity of illness.