one is based on an entire industry of people working in so many conflicting fields that it would boggle the mind if they could all be bought, and the other is based on one person who built their fame on being contrarian without a lot of evidence.
I think the question still makes sense, why people are willing to ignore a ton of evidence from a lot of different unaffiliated people and focus on one article by one person that really doesn't add up to much of an argument - I think the answer is just that this is what they want to hear, so it must be right.
The claim isn't that everyone in nutrition etc is bought off. You simply don't need to do that.
If you're in the sugar industry, you give funding to people investigating how saturated fat causes heart disease. You support organizations that back up your preferred theory. These orgs run media campaigns, slap a "heart-healthy" label on food products, and sometimes fund research. Forming popular consensus on "fats = bad" leads to additional funding from government or other charitable causes.
Increased funding leads to an increased density of scientists working on the problem, which in turn increases the legitimacy of the field, especially among people just getting into their careers. If it's common wisdom in the cardio field that saturated fats are the worst cause of heart disease, that's where they're going to focus their efforts.
It's one of those things where you simply don't need to buy anyone off. You just put your thumb on the scale early enough, and consistently push popular opinion toward a direction that's beneficial for you.
if somebody can find an even worse cause and they publish it, they stand to found an entirely new field - the incentives are to prove the entire existing field wrong. nobody would hesitate.
I think the question still makes sense, why people are willing to ignore a ton of evidence from a lot of different unaffiliated people and focus on one article by one person that really doesn't add up to much of an argument - I think the answer is just that this is what they want to hear, so it must be right.