But it's not about complexity really. I think it's more caused by the deeply ingrained superiority complex in most russians. And just in case, most russians != every russian.
You could live there until very late in life never needing to know more than a few sentences.
so they either don't learn native language of the country where they live or learn it to bare minimum
My hypothesis: I understand russian and register cases like this easily. Otoh, I don't understand Chinese, so the ones with whom I have ever had any communication, are the ones who learned any of the languages I understand. Similar story with Spanish, my level is ~A2, so there's bias here too, although slightly less prominent.
Do you understand russian?