For years, they requested files from my web site. I got single digit referrals from Yandex over those same years. So, I went to yandex.com and looked up some of the things my web site has info on (combinatory logic, for example). I got really spammy and scammy links from yandex on those subjects, and others that I've tried.

I just used my own judgement on it.

Sometimes Google gives spammy links as ansewrs too. So why don’t block it altogether?

The key here is "sometimes" versus "all". In my estimation, Yandex gave nothing but spammy or scammy looking links, and certainly nothing worthwhile. So, I decided to futz with them.