I'm going to quote a line from a movie here that is pretty accurate here.
Don't you know a man being rich is like a girl being pretty? You don't marry a girl because she's pretty, but gosh, it sure helps, doesn't it?
It's a natural instinct for a woman to want her and her children to be taken care of. Financial security and stability are what we want. For hundreds (probably even thousands) of years, girls were married away to richer, older men whenever possible. Marrying for love is a very new concept in the history of humans.