So I have a pet theory on studies like that. There are many things out there that many of us take for granted and as givens in our daily lives. But there are likely equally as many people out there to which this knowledge is either unknown or not actually apparent. Reasoning for that can be a myriad of things; like due to a lack of experience in the given area, skepticism that their anecdotal evidence is truly correct despite appearances, and on and on.

What these "obvious thing is obvious" studies accomplish is setting a factual precedent for the people in the back. The people who are uninformed, not experienced enough, skeptical, contrarian, etc.

The studies seem wasteful upfront, but sometimes a thing needs to be said aloud to galvanize the factual evidence and give basis to the overwhelming anecdotal evidence.

Literally this article is about the study. Your “well-known” fact doesn’t hold up to scrutiny.