And also absolutely trivial to detect automatically. The fact that Google doesn't do it proves they don't give a shit about improving search quality beyond superficial efforts whose main objective is just to make it look like they do. Maybe the fact that most spam sites have Google Analytics & Ads has something to do with it?
I mean spammers can (and do) get more fancy with e.g. detecting the source AS and its owner for cloaking, but I guess the spammers here are using geo location for a veneer plausible deniability that they're not specifically targeting Google.