Why are ladies' and men footwear so different?

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I'm wondering why are shoes made for women and men so different in design and shape? If a man appears at a business event or at a wedding in sandals (and I don't mean flip-flops) he is considered to be inappropriately dressed, or even rude. On the contrary, if a woman wears hiking shoes or running sneakers, she is considered as un-feminine. I agree that ballerina flats or pumps would look to say the least odd on a man, but I'm not taking things that far... I'd simply suggest there should be more openness for more open (pun intended) shoes for men, especially in summer.