Because the only things it does tangibly effect are your mood and mental perspective, things that are entirely subjective and do not have concrete metrics that

Because the only things it does tangibly effect are your mood and mental perspective, things that are entirely subjective and do not have concrete metrics that can be used for measurement, especially when comparing that between different subjects. The only really noticeable effect of microdosing is at the end of the day you might notice you feel it was a really good day and you're happy. The thing is though this isn't distinguishable from someone simply having a good day and feeling happy. The data collected in this study would have essentially been irrelevant noise, based more on the aggregate of day-to-day experiences of the subjects rather than whether or not they received a placebo. Microdosing inherently is indistinguishable from a placebo effect as far as empirical measurements go. If the participants who received a microdose were able to somehow measure their experience with a different result to those in the control group, then they weren't microdosing, they were actually tripping.