I don't know what started it but I can see why it continues.
Human nature, imo, looks to firstly protect your own, then your outer circle and only then does it look beyond. So if you accept that there is an inherent selfishness in human nature, it makes sense that those in power hold on to it. And I don't think that selfishness is necessarily a negative in that regard. If power brings protection, then it would kind of be daft to give it up.
We bind ourselves quite willingly or unwittingly in society in order to have protection but in order to do so, give up a degree of freedom and power and in doing so, afford more power to those in charge, trusting that they will abide by the terms of that social contract.
So even historically when women were considered legally as less than men, there was an obligation on men to provide them with support in return. So women would enter marriage for the protection of men and their ability to provide and men in return would gain an heir. When you look at a more modern society and the way that we compete for resources, physical strength isn't such an advantage. So women don't need protection (assuming of course, that they once ever did) as they're now able to obtain food, shelter themselves, protect themselves.
So women want to renegotiate the social contract but that involves either overthrowing men, who don't want to give up their power or advantages, or persuading men that working together and equally will result in gains for all. The reality is that for a lot of men, there wouldn't be any gains but nor would there be any losses so we're back to the selfish element but now in a negative sense.
I don't think that men want to come to the table to have the discussion sadly but I do think that the more women insist on the discussion, the more likely it is to happen but it's a slow process.
God, that was boring but I've typed it now so may as well hit post.