I don't know how to describe it succinctly, but I find there to be a stark category difference between what the article talks about and what you mention. In particular, the former is what I appreciate as a user, the latter is what I hate.

> Furthermore, at least in my experience, longer product pages don’t actually have a significantly negative impact for on-site conversion rates.

That's probably because e-commerce stores aren't commodity. The user is going to convert anyway, even if they hate every minute of the experience.