Why do you think that? Compare it to the type of customers you attract at different stage of building a product: your first customers are always the most passionate, most valuable customers. As you broaden the customer base, you attract people that are way less into your product. Female founders are still a very small group, only the most passionate, most courageous, most talented ones are currently considering becoming entrepreneurs. Once being a female founder is the new normal, pitch to funding rates between males and females will be much closer again. Having said all that, this is just a theory based on anecdotal experience.