① Language use is an ingroup signifier, and by writing like this, they are identifying themselves as the sort of person who knows Putin's career began in the КГБ; knows that the Rasputitsa foiled Napoleon, the Mongols, and Hitler; has read enough of Thucydides to know what arguments the Athenians used to justify mass-murdering the Melians; and doesn't particularly care about capitalization, punctuation, spelling, or grammar. Perhaps on rereading the comment thread they feel self-satisfaction in the contrast between their knowledge and my floundering ignorance, or perhaps they are hoping to signal to other people who share their background. Moreover, this sort of shibboleth is a fairly reliable signal; outgroup members who attempt to imitate the ingroup will invariably slip up and use the wrong punctuation mark or something.

② By referencing bits of common knowledge rather than explaining each one, they can lay out their theory of the causality of these geopolitical events in three lines rather than six paragraphs. This is both less effort to write and, for their ingroup audience, less effort to read.

In both cases a necessary condition is lack of interest in communicating with the outgroup.

I just did something similar (though, I hope, less extreme) in https://news.ycombinator.com/item?id=30505214. I figure that if someone doesn't know what CNG, Fischer–Tropsch, Teamster OOs, Jet A-1, fleet organizations, bunker fuel, etc., are, they can google them; if I tried to explain them it would just get in the way of understanding my already overlong sentences with too many nested clauses which frequently overflow the stacks of the brains of the humans.