Here's the minority's perspective:
1) Why is it required that there can be no more than 20% women in a tech company?
2) Why is it required to have a minimally diverse company?
If you look at these two questions and just say "hah! that's not the same thing at all!", then that's why.
Well, they're not the same thing, because nobody is claiming 20% women and minimal diversity is a moral imperative. There aren't executive-level staff in major corporations who are paid handsomely to ensure a 20% female staff. If you're arguing there is some kind of secret covenant amongst the shadowy bro-network for a fixed 20% women quota and minimal diversity, you'd need to provide some proof of that. Aside from that you haven't really addressed the questions I asked.
I've noticed a real inability (or perhaps disinclination) to speak about these issues in a straightforward way.
If you look at these two questions and just say "hah! that's not the same thing at all!", then that's why.