1. The general public is very interested in the results, and so there's a lot of motivation for people to misunderstand or exaggerate the results in conveying them to the general public.
2. The connection between nutritional intake and results is very complicated, and ties into pretty much everything about how a person lives. The data is very noisy, and so it's hard to get good results. Other sciences, it's a lot easier to get clean data.
And yet the needle moves forward, slowly. Ideas get refined, the details get filled in, and bad ideas get tossed out. We go from "fat = bad" to "some fats are bad and some are good". That's the natural progression of science. I'm sorry Scott Adams doesn't like that's how science works, but it's the best thing we've come up with so far.