The main reason is that Shi Naian was jealous of Gao Qiu in history, who clearly had no ability, but had been a high-ranking official for twenty years because of his good football skills. In order to vent his grievances, Shi Naian turned the villain in the book into a high-ranking official. Named Gao Qiu.
Gao Qiu in history was not as bad as described in the book. At most, he was in a high position but not very capable.
Originally, with Gao Qiu’s fame, he was not qualified to sit in a high position, and he did so for twenty years. But who made him lucky? The person sitting on the throne was his golf mate.
With this relationship, Gao Qiu became a close confidant of Song Huizong. In order to let his little friend climb up, Song Huizong gave Gao Qiu a good opportunity.
Ask Gao Qiu to go to the border to get gold, and then come back, so that his friends can be promoted to a high position. Finally, Gao Qiu went to Bianguan. Perhaps because of his luck, he won several battles at Bianguan.
So Gao Qiu relied on his achievements in winning these battles and was successfully promoted. In the end, his official position became bigger and bigger, and he became the palace commander, responsible for taking charge of the imperial army.
Compared with Gao Qiu, Shi Naian's official career did not seem so smooth. Shi Naian looked at his own official career, and then looked at Gao Qiu's official career. It is believed that Gao Qiu had no fame or any political ability, but he became a high-ranking official because of his good football skills.
For an opportunistic person like Gao Qiu, Shi Naian said that I am jealous, so I can't defeat you in reality, but I can discredit you in the book.
So Shi Naian created in his book a young hooligan who was highly valued by the emperor and entrusted with a big job because of his good football skills. But instead of doing practical things well, he went around killing loyal people and bewitching the emperor.
So Gao Qiu, who had no major faults in history, became a notorious figure because of Shi Naian's Water Margin.