1. Western feminism
2. Men want companions, but not competitors.
Eastern European women like to be women, they are feminine. Well, cooking, housekeeping etc. is not a primary concern, it's the attitude of women that makes them so attractive to western men.
Although there are some men, who think that their russian wives should be extremely grateful for arriving in the US, such men expect them to clean, to cook, take care of them and their kids from previous marriages etc. and not to ask for much in return, thats why they bring Russian women to the US. They definitely were misinformed about Russian women and Russia. And usually what they finally get is a divorce right after a woman gets her Green card.