People complain about this when they come to Scandinavia too. (not enough smiling...).
Personally I often smile to strangers though, because I feel like it - it's my personality.
Perhaps the cold climate and dark season makes people more reserved and a bit grumpy. It is something all Northern countries, including Russia, have in common.
However when a Scandinavian person (or no doubt a Russian) smiles it is because they really want to and it's genuine. I can't stand phony smiles.
Finland is quite extreme in this respect. They don't smile much and they don't EVEN talk much.
But they are very nice and genuine people.
I noticed that English people are a bit more friendly and kind towards strangers compared with Sweden. I appreciate this a lot. For example if you stand with a map and look lost, then someone will come up and offer to help.