When Prophet married among those people the whole tribe became friendly and many people accepted Islam. So his marriages were not for sensuous reasons, but for the benefit of his community. Polygamy is very much associated with luxurious life style with palaces and a lot of food and fun. The Prophet's lifestyle was very different. Lot of improper suggestions are made by some non-Muslims regarding the Prophet's polygamy to attack his blessed personality.
Promiscuity is a weakness.
Islam hates weakness in Muslim men as well as women. Freedom to have multiple sex partners is most definitely not the reason for polygamy in Islam. One should never associate the Prophet's polygamous life with the life of many rulers or other people who practice polygamy for sensuous reasons.