My half-believed conspiracy theory is that "seed oils bad" is a psy-op from the corn/HFCS industries. I don't have hard data here, but it seemed like in the late 2010s people were converging on added sugar and especially HFCS as the thing which is truly messing up health. I can't help but wonder if the corn industry saw this, panicked, and began seeding (no pun intended) the seed oil meme among influencers.

I don't have evidence for this specifically, but there's certainly a long and documented history of both a) influencers suddenly adopting a new party line in response to a paid campaign and b) shitty policy specifically for the influential corn industry (ethanol subsidies, e.g.)