You almost answered your own question. Why do all societies recognize marriage between one man and one woman (and sometimes polygamy, which is a minority position)? Because it's natural. It is of the natural order. People intuitively understand that marriage between one man and one woman is the best way to raise children and is the proper context within which men and women should unite sexually.
What other institution could be proposed for the raising of children? The question itself is absurd.
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