Well the story explained it. It is for the wellbeing of the country. An emperor has to think about his country first before anything else, even if he doesnt like it, he has to.
Children—> so there would be a successor and also that the royal blood would go on. in ancient time a lot of children die at a young age. In the palace there are also other threats than illness.
Concubines —> their family wealth and power helps to stabilize the country and also support the royal family. There are also political marriage.
It doesn't matter if the Emperor loves his first wife as the Emperor it is his duty to make sure that he has many heirs to surpass him after death. Think of it like a lion pride. The more cubs a lion has the stronger his pride is. Doesn't matter that the females do all the work his job is to protect his pride and have cubs. The Emperor's job is protect his country and have many son to choose from when he hands over the throne. Because there is so much intrigue in the harem the princes are often the target for death because the woman that gives birth to a son and has it survive has a chance to rule by her son's side. So he has to have sex with everyone of his harem at least once to solidify alliances, and if they give birth to a boy it means her family moves up in power. The Emperor can't protect his empire with out the alliances these women bring and the power of their families, so having one wife is a death sentence to the Emperor and his family, literally.
I don't know why, but I also hate the emperor. Based on what I know, emperor must be ruthless and smart when it comes to judgement but haa it's really pissing me off. And he could have not just have sex with other concubines like threaten them not say a word or they'll be dead bit still he had sex with a lot of them! If it's really true that he doesn't like them and only the fl,. why will he have a lot of child and concubines. (︶︿︶)＝凸