From my observation, the discrepancy in spending habits between men and women has a lot to do with opportunity in life and social standing. It is well known that people from disadvantaged backgrounds usually spend less wisely. This is why winning a lottery rarely makes one rich.

Women simply do not get the same rewards for work they do. I don't mean just financially but generally. I read a very interesting account from a trans man and his experience of transitioning. The change was shocking. This individual after becoming a man immediately received recognition at work, even though in their personal opinion their performance didn't change. As a woman, he was told to be lucky to have a good job, while as a man he was told he earned and deserved it. He received bonuses never given to him when he was a woman. Even small things like social meeting improved for him, things like people laughing at his jokes etc. Then there was no bullying. All sexual harassment stopped, he no longer was bullied for unshaved body or not being dressed well etc. It was exactly the same person, all that changed was how people perceived this individuals gender.

Women are told that their value comes from how they and their environments compare to others. This is how women establish a hierarchy between each other. If you have a pretty house and you look great your peers respect you. If you do not you are a laughing stock. Reputation matters to people more than income and for a woman, it's not enough to do a good job, you also have to look the part. Marketing exploits and perpetuates this which is completely unethical in my opinion.