User blog comment:Kirkburn/Technical Update: May 17, 2017/@comment-5973717-20170521181059/@comment-197.218.91.112-20170522145018

It is obvious why, Politics. Ukrainian - Russian relations aren't the best, and some may feel irritated by seeing such text in an interface.

Linguistically speaking, the Russian fallback makes sense (except in cases where it can be confusing due to cognates) because many Ukranians may understand Russian.