I think you are mischaracterizing this meta-analysis. First, a meta-analysis is never about just trying one thing; that's what a single study is for. A meta-analysis looks at many studies, over a long period of time and tries to find consistent patterns that emerge from the whole. That's how we try to systematically figure out if results are by chance, or if there's a real effect. The pattern these authors are pulling from all of these studies is there is no real effect. When you find no real effect over many studies for a long time, you inevitably have to confront the question: is what we're trying to do possible?