Evolutionary biology tells us that it falls down to who is doing the picking of the mate. With birds, the malse have to show their wonderfulness to the female in hopes that she picks him. Remember, she has to sit still long enough to allow him to do his thing and not fly off.
We have a culture a tad more complex than the birds and the bees. If you think about it, the women need to attract the man who is going to, hopefully, care enough about her to stick around for some 15 years or so because our young need more care. We don’t kick the babies out of the nest after a few weeks and start the whole thing over the next season. For better or worse, culturally, women have had to rely on the man to protect and provide for her and the brood they produce for years, not just a simple spring and summer. The more men she attracts to herself, the better her chances are of finding the one that she hopes will offer the best life for her and the babies she’ll have. Sound cold and unromantic? Yep.