Because I'm not a scientist. And anyway, the reason they didn't include this is because back in July 2016 when this review was written, there were no published

Because I'm not a scientist. And anyway, the reason they didn't include this is because back in July 2016 when this review was written, there were no published placebo controlled trials. The Kelly trial was only published in Nov 2016. Presumably newer meta analyses will take this into account.