Why? Well, for one, women get paid much more overseas to play than they do here, and are treated very well. Cars, houses, food, etc. are paid for as well as your salary.
When Hammon was left off the initial 30-invitees for the US Team (later asked to try out, but with little chance of making it), even though she was runner-up in WNBA-MVP voting last year (does that mean anything?), she decided to use her Russian passport to play.
Its an interesting story that involves money (lots of it) and representing your country, or lack thereof.
You be the judge on her story...