There are other, non-nefarious reasons. 1. They make excellent student projects. Part of this is cheapness, sure, but part of it is that meta-analysis can be d

There are other, non-nefarious reasons. 1. They make excellent student projects. Part of this is cheapness, sure, but part of it is that meta-analysis can be done relatively quickly. Some observational studies will take years to complete - in the meantime, your Masters student needs something to do. 2. They are often "Step 1" of a number of study designs. For example, if one is eliciting priors for a Bayesian analysis, or in my case trying to parameterize a theoretical model, "Is there a meta-analysis on this, and if not, can we do one?" is one of the first questions asked. 3. It allows participation in a field. For example, I have thoughts about some aspects of clinical medicine. I am unlikely to ever run a clinical trial, what with not having a position in a medical school. I can however perform a meta-analysis of trial data as well (or possibly better) than the people performing the studies. Running a study and conducting a meta-analysis are not necessarily the same skill set.