There's actually some historical context for this untrue way of thinking.

France, 1873 Paul Broca, a French physician, decides to weigh some brains. And women's brains weighed less than men's brains. This is part of his research into crainiometry in which the size of the brain is used to understand a mesure of intelligence. Bigger brain weight = more smart.

We now recognize crainiometry as a pesudoscience.

Then another French academic Gustav Le Bon uses Broca's research to further engain that not only are women's brains small causing them to have the big dumb, women are in fact more similar to gorillas in brain size. Thus, women are uncivilized, akin to children, and MUST be under the care and control of men who are CLEARLY more intelligent with their big brains and, naturally, should control and run society.

Broca did not take overall body size or age of the specimens into account when originally weighing the brains. The male specimens were younger and larger to the female specimens who were smaller and older. Brains tend to shrink as we age.

So, not only was this flawed science, based in flawed measurements, thay have been readily disproved, we're still struggling to undo this as a belief.

History rant over.