It's an intersection of (people interested in tech) & (people interested in entrepreneurship), both are male dominant though one could argue for a close to equal balance in the latter if you consider any side business entrepreneurship - many women silently start lifestyle businesses and never get recognition for doing so the way rockstar CEOs do.

Thinking about it YC's focus on hacker-founders adds another % into the mix too, the percentage of women programmers - I think it's simply math, multiply through and you get the absurd weighting seen at SUS.