More can be said for sure, but here's an answer thread featuring me and /u/Iphikrates on a very similar question.

Thank you to lcnielsen, great comment! While reading it, I had a follow-up question occur to me, both that comment and the OP in general.

While legacy is certainly a massive part in the bias, is it also possible that the settled-nomad dichotomy is at play as well?

As far as I can remember my uni classes, most settled peoples had a very lowly view on nomadic peoples, and for some living closer to these groups, outright feared them (e.g. China). Chinggis' rule seems to be far more lenient than most conquerors' (that is, if your city surrendered), yet it is rarely remembered for its tolerance for religion or opening of safe trade routes. Are there any reasons to to believe this attribute plays into this as well?

Sorry, but we have removed your response, as we expect answers in this subreddit to be in-depth and comprehensive, and to demonstrate a familiarity with the current, academic understanding of the topic at hand. Before contributing again, please take the time to better familiarize yourself with the rules, as well as our expectations for an answer such as featured on Twitter or in the Sunday Digest.