The Obstacles to Diversity in VC Funding

In the US, over 40% of new businesses founded every year are founded and led in many cases by women. But there's a trickle that goes to that very large pool - what do you think are the hurdles? So, why is that? And are there solutions we can approach? For instance, I mean, we were mentioning before boardrooms, much improvement has been achieved by encouraging or even mandating quotas. Is that an approach that can be used in VC funding?