The studies that claim benefits from diversity are almost always correlation, not causation. It's easy to see how reverse causation could be at play. Companies that are more profitable can afford to have diversity programs. This fact can be reframed to make it look like the diversity came first and caused the higher profitability.

When DEI studies were first being touted I used to ask to read them. I thought that perhaps I would eventually find one that actually had any rigor behind it. After reading dozens, I stopped asking. It seems that rigor is not required. Just a headline that resonates with key constituencies.