The first reason. The percentage of female population in Ukraine is much bigger than the male.
Many of them are interesting, smart and wealthy gentlemen.
In Europe the situation is quite different. Ladies marry between the ages of 30 to 40 years old, the guys even later. People create a family consciously before checking out their feelings. And only then they build family relationships. Therefore, a woman knows that she has a right to make choices. So many Ukrainian women that by local standards were not beauties said that only abroad, they were able to feel like real women! In Europe for a woman of 40 years old, the life has just begun. And in Ukraine, single women at this age are already quite confident. Because we have traditionally believed that after 30 years old a woman has no chance to start a family, meet an interesting man. Many women in Ukraine want to marry a foreign guy just because Ukrainian men I do not consider them worthy of their attention after 30-40 years old.
Of course, often one of the reasons that Russian women decide to marry abroad is economic problems and a desire to relocate to another country, but it is quite a small percentage.