"Pretty sure most of the fairytales were written by men. A lot of them end with a handsome prince or knight rescuing the princess and marrying her, so there's probably some wish fulfillment in there. They were also written at a time when women were considered lesser people to men; if the eldest princess had any younger brothers the oldest one would inherit the throne instead of her, and if there were no prices then the princess would need to marry and her husband would become the king. That changed over time and didn't always get followed, especially if the queen was strong enough and had enough support. For the monarchies surviving today in my world, as far as I know they're all strictly by birth order regardless of gender. England is the big one, and they have a queen right now. The next three will be kings though."