Your question is indeed reasonable and I would like to answer your question with my wisdom and knowledge of understanding from upanyasams. 

First of all, according to the sasthram and vedam even men are not allowed to have more than one wife and great examples of these is shivan and parvathy, rama and seetha and off course sages and munivars. 

The reason why they have these is because according to previous yugas they allowed it because their way of living is different as they had long life but munivars and rishis decided not to permit this to kali yuga for the goods of this world. Also, even though Draupadi married 5 pandavas, it is because of her boon and although pandavas had other wife, only draupadi is to be the queen of indraprastham. A husband cannot share his love with more than one wife and an example of this is Dasarathan where he had more love for Kaikai which she utilised to make her son the king of Ayodhya. 

Also, think about it yourself how a girl will be when she shares herself amongst men? It is not good and as Draupadi and Thara were not ordinary woman they were able to manage. And although Draupadi married 5 men, no one was able to stop her from that disaster so what would be the state of ordinary woman? 

You should read or hear about Draupadi’s one of her previous birth as Nalayini. Then you will understand. And remember woman are greater than men because they attain moksha by helping them and looking after their husbands so sastra or dharma wants woman to do their duties.

I hope I have answered your question.

Thank you

Sakhi