I suspect this is to deter Russians from coming home for the Orthodox Easter which is way more important than in the West.
Summer or New Year are the times when Russians are more likely to go to visit their relatives and friends.
Oh, and by the way: Russia has state holidays from Jan 1st till Jan 10th (+/-, every year is slightly different), which makes it a lot easier to meet everyone.
Easter does not have any state recognition in Russia, so everyone would be quite busy with their regular errands, I guess.
Summer is a good time to visit because of the mild climate, and New Years', because it has always been a big holiday, culturally.
For religious Russians abroad there are Orthodox churches in almost every country, even in Thailand and Cambodia.