I think part of the reason why girls are more flexible than guys is because on a day-to-day basis, they’re not afraid to spread their legs. Some guys never spread their legs at all, due to fear of those nuts getting hurt. A girl might spread her legs once or twice a day, putting on pants for example, or straddling onto a bench.
One day may not make a difference, but over time, day by day, those leg muscles get more and more flexible. It allows women to spread open their legs to incredible angles that most guys can’t.