This is actually because of a cargo cult fetishization of longer texts. As most people moved to rapid consumption of many disjoint sound bites, knowledgeable people read more than headlines. Those who then wished to emulate these decided that anything long is meaningful leading to a fetishization of “long form” prose.

You’ll see a pretty high correlation between fans of “long form”, readers of The Atlantic and The New Yorker, and political inclination around being perceived as erudite.

It’s one of those cargo cult mixed with a measure becoming a target.