And how much were they sold to boys cause idiotic families pushed them only on the boys?
Sure, but what was Lego supposed to do about that? They could have started a multi-decade advertising campaign to try to change social perceptions of girls vs boys toys, and maybe that would have eventually paid off. Or they could just make specific "girl" Legos.
As a business that wants to make money, they went with the latter option and it worked really well. And realistically, I don't think we should expect individual companies to try changing society instead of just targeting their products to society as it is.
It's also worth mentioning that when Lego did studies on it, they found that girls played with their toys differently. The girl Legos were designed to be based around a different type of play, that was supposed to be more appealing. It wasn't as simple as this is in pink and has girly lettering on the box.
This was my first thought as well, so I looked into it. Turns out JSAUX does provide a range of 3d printable models that can quickly connect to the modcase (as well as a template for modeling new attachments). You can see the models here on JSAUX's printables page.
Included models for it include:
Edit: Here's the model for designing new attachments