You are also making the assumption that studies and metastudies are not trying to sell you something or that the authors aren't trying to prove something that the science doesn't support.

I don't think every study is completely corrupt. I wouldn't call it an assumption as much as an assessment that a lot of studies seem to agree with reality pretty well.

Pragmatically I suspect this might be because most of the market don't actually read these things, and are just as happy with made up bs.