Easy. They don't want their women too smart or God forbid, too ambitious.
This is sort of related, but there is a lot of research and a lot of papers written about the increasing gap between the rich and the poor in the USA. And one of the contributing factors is that 50 years ago, by and large you had a stay-at-home population of women, married to income-earning men. That then began to change but overwhelmingly the men made more money, and there was often the effect of a high-earning man lifting a woman a level or more up from her socioeconomic position. For example, the much more common scenario of executive men marrying assistants and so on. What has changed with the influx of women into the workplace is that we have become a much more class-defined society. Meaning, the professional class tends to marry preferentially within the class itself. Lawyers married to other lawyers, doctors married to doctors, accountants, etc. And as time goes on, this will just become more pronounced.