It's ironic, seeing tons of exclusively russian-speaking immigrants not being able to learn the native language after decades living in the country.

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.

I was surprised as well living in Hong Kong that many kids grow up never learning Cantonese being born there (Non Chinese heritage). Their parents spoke their native language, and they learned English in a private school.

You could live there until very late in life never needing to know more than a few sentences.