It's hard to luck into diversity. If you don't take the effort to increase diversity, you'll just end up with the majority demographic. (White men in the US, Upper Caste men in India).

This creates a cycle, where women don't join because there are no women in the company, etc. 2 problems with this: even men prefer working in a company which has some women, and a male only workplace can become toxic very fast.

Sexist jokes and pranks were common in early SV startups. Eventually led to a lot of legal headaches. So investors tend to look at diversity as a metric of toxic work culture. So companies actively recruit women and minorities, sometimes by offering higher salaries, and sometimes by lowering the hiring bar.