The studies you’re talking about were small, and typically self reported by the pet owners. If they were a human study they wouldn’t be enough to go off of.

Best research paper out there is actually looking at the studies in question, and isn’t specifically for cats but pets in general: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9860667/

And it explicitly states that much of the data was gathered through survey, not a controlled study.

Imagine if we decided that ice cream for breakfast was healthy because we sent out a bunch of surveys and people said they saw health benefits.