Exchange theory has a good, easy explanation for all this. Class affects how we are brought up, how we speak, our values, our expectations, as well as our life experiences. We come into contact with them much more frequently than with others. We tend to marry them. If we choose someone else, then it is likely that the female will be of the lower social class.
Males like to dominate.
A wife of a higher social class might be more difficult to dominate. Traditional sex roles had the male being the provider. When a woman married, she married her standard of living. A man did no such thing when he married. The class background of his bride had little direct influence on his prospective standard of living.