https://www.phoronix.com/news/Russian-Linux-Maintainers-Drop
So much for freedom kekw
According to this old commit, maintainers are dropped from that file if they fail to respond to emails:
https://lore.kernel.org/lkml/Y2JfoWTaAW6QjavL@kadam/T/ (https://lore.kernel.org/lkml/Y2JfoWTaAW6QjavL@kadam/T/)
And one can imagine various reasons why Russian kernel maintainers in particular might be unavailable or have other commitments, or even have requested this themselves. So there are numerous possibilities and not enough information to draw a conclusion from what's published I think, although it's a good story.
Edit - no, sorry, it seems I was being too generous in interpretation from subsequent reports. I personally don't think defining people by nationality or any similar ethno-religious categorization is helpful on an individual basis even if generalizations might be made. There are supporters of both sides (and no side) on each side in reality.