Throw in some nice cherry-picking results, human psychology where the diet didn’t fail you, you failed the diet so people aren’t willing to speak up when it doesn’t work for them, and in todays day and age paid commenters that will bombard YT videos with fake comments both pro on your videos and anti on videos by actual scientists who have studied this stuff and have seen remarkably similar results for decades.
After all, there’s not much money to be made in “eat foods. Mostly plants. Not too much”. Especially when on the other side it’s not just processed foods but even the meat and dairy industries that are massive operations making a lot of money (with some hefty tax breaks and subsidies thrown in to boot).