They don't censor results for western sensibilities the way Google does. For example, if I search for a certain wrongthink blog I'm not supposed to be reading, google gives me literally 10 pages of results (I checked, out of curiosity) pertaining to a movie that shares its name--none relevant to the blog. Then when I tack on one additional specifier term (like part of the domain name, or the word "blog"), google magically relents and shows me the relevant results, as if to say, "ok, I'll let you search for that naughty thing, if you're 100% sure that's what you really want." Thanks, Google! By contrast, if you search the blog by name with Yandex (and DDG), it's on the first page.
Also, Yandex never nerfed the facial recognition features of their image search like Google, Bing, and the rest did. (I assume they did this because women complained it made it too easy to find their old nudes.)
Anyway, Yandex is good competition, and while not so much a complete alternative to Google, it's definitely a useful adjunct to it, and it's popular on /g/ for that reason.