Because they think PUFA are ok to ingest. The seed oil manufacturers began pushing these types of oils as healthy around the time of WWII. They are very damaging and affect the thyroid adversely.

I follow Ray Peat because with the advice given I was able to reverse a case of NAFLD by getting rid of PUFA, replacing it with coconut oil and butter. and increasing carbs in the form of fruit or sometimes sucrose as well as increasing protein to 100g /day.

"Animal proteins, and fruits, because they contain the lowest levels of toxins, should form the basis of the diet. Not all fruits, of course, are perfectly safe--avocados, for example, contain so much unsaturated fat that they can be carcinogenic and hepatotoxic.

Protein deficiency itself contributes to the harm done by toxins, since the liver’s ability to detoxify them depends on adequate nutrition, especially good protein." http://raypeat.com/articles/articles/vegetables.shtml

http://raypeat.com/articles/

Kate Deering has a book out that covers Peat's dietary recommendations https://katedeering.com/book/