In the "THe VILLaIN aRC oF VANiTY SiZINg" section, vanity sizing is framed as marketing strategy which is successful because of the psychology around that - linking out to https://www.sciencedirect.com/science/article/abs/pii/S10577... for more detail.
It certainly wouldn't be the first time the most profitable marketing strategy is unrelated to aligning with what's optimal for the consumer.
This is the weirdest section, and is just unnecessary virtue signaling.
Women don’t buy their real size because it makes them feel bad -> market pressures companies to address that by doing vanity sizing -> brands bad
I cannot comprehend that jump in the logic.
Of course education could help about this and other psychologically manipulative tactics by corps but such kind of education is heavily frowned upon for being seeing as anti-capitalist and (more propagandistic) as un-american, so there is zero of such kind of education.
Translating the confusing science speak, basically:
Appearance self-esteem takes a hit when they don't fit in a size. They take it out on the clothes: "I hate their stuff, they suck." They buy more of other stuff to compensate for the hit, whether non-sized accessories (I am pretty) or book/tech (I am smart even if I don't fit).
People confident in their appearance are immune to the effect, and simply think it's sized wrong or runs small.