Well for one, in the press conference when he announced the CDC’s recommendation to wear cloth masks, he emphasized that it was a voluntary measure and then added he wasn’t going to do it. People look to their leaders for guidance. How many people refused to wear a mask despite the CDC’s recommendation because the president felt the need to throw in his own opinion with his experts’ recommendations.
Sample size isn’t the problem. The problem is we don’t have a control group to compare against. Ideally, you’d compare people with micro plastics to people without them, but those people don’t really exist anymore.