Men gain social status and financial stability with age while getting weary of their wives (they once were attracted to), so by certain age they start craving change - the last chance. The women who post on these web sites (if they are real, not a scam) are desperate for stability. They are often looking for someone for whom they will be that last chance.
Alcoholism and economical instability in Russia and other countries of former Soviet Union make it tough to find a "decent" man...
However, because of the cultural differences they rarely find what they are looking for in Western men. West has its own problems. I feel sorry for them.