Because ORD already has nonstop service 6x a week to WAW via LO (1x a week goes to KRK), and Moscow doesn't?
The number of people from any ethnic group traveling back to "the old country" tends to drop from generation to generation. Foreign born are most likely to travel, first generation US less so, and their grandkids even less likely to go back.
There's a huge Polish community in the CHI/MKE area, but I'm not sure how many of them are immigrant vs. first, second, or third generation US born.
If there are more Russians who are immigrants or first generation, they're more likely to be traveling back and forth.
Also, the way that the Russian economy is going, there's likely to be more business traffic in that one market than there would be trying to share a market with LO (who codewhores with UAL).