Jin Gu might never understand but Jin Kai never had fatherly love for him in fact, Jin Hao and Jin Hua also didn't have that kind of feeling towards their real father, and for once unbeknownst to them, they actually had something in common.
It happened because Jin Gu had too many children to raise and they came from different women and every woman fought for her father so one can imagine the relationship between siblings would not be good, Jin Hao and Jin Hua were the only exceptions.
Jin Gu treats women like collectibles, if he likes them he will treat them well but if he gets bored he leaves them and moves in with interesting new ones, he also treats his sons and daughters like chess pieces or investments that he can use in the future for to his own advantage that he inevitably does not have a deep relationship with his children which he never realized because everything he cared about had to be left for his children to control and obey.