That is ridiculous. It is not as if polygamy was installed by the Prophet Muhammad as an religious institution with a specific purpose. It existed before him not only in Arabia but all over. The only thing the Prophet did was to limit the number to four.

So, it would be more fruitful and accurate to ask why Islam limits the number to four. There is no Islamic "reason" for polygamy. There is a natural "reason" that polygamy existed in the world, and it probably has to do with the gene pool and such. The biologically 'successful' members of the species reproduce themselves more. Every living thing has the urge to do this. This is how Allah has created natural life. The more wives you have, the more you can pass on your genes, and the bigger group you have under you to back you up when you grow older. It makes sense.

So, if we want to talk about reasons for Islamic institutions, we need to talk about its limit of polygamy, not polygamy itself.

All these so called Islamic 'reasons' are just crap that Muslims came up with to respond to continual criticism from European colonizers.

Europeans went to monogamy because Apostle Paul taught them that sex is intrinsically sinful, so one must limit the sin to one mate, since man is originally sinful and helplessly weak against his lust. You can read that for yourself.

That is why later, Nietzsche claimed that Christianity was an anti-life religion, since it starts with the premise that earthly life is an irredeemable evil. Therefore, anything that reproduces life must also be evil. So, the monks go celibate.

Nietzsche was right about that.