Actually, there are reasons, and lots. Go read the literature. Really.
One of the best study is International Preferences in Selecting Mates. This is a large study (N=9474) with samples from six continents, from cultures with monogamy and polygyny, etc.
One of the best study is International Preferences in Selecting Mates. This is a large study (N=9474) with samples from six continents, from cultures with monogamy and polygyny, etc.