It's also hard to learn and practice, with non-standard characters. It might be simply too expensive to support it at this point.
Russian is one of the easiest languages to learn though, the game supports much more complicated languages, I don't buy for a moment that this is a factor.
Seems very unfair, there are plenty of Americans that speak Russian as their first language, not to discount the non-Russian countries that predominantly speak it.
Hard to not see this as virtue signaling imo.