At that time, for Wei, where Cao Cao himself was, although he had been able to grasp some information about defending the country, some old ministers of the Han Dynasty did not loyal to him, but chose to rebel. Even Emperor Xian of Han wanted to kill him and regain his rights by creating some opportunities, so he was not particularly stable to Wei.
For Shu, Liu Bei's territory is rich in products, and because of geographical advantages, it is easy to defend but difficult to attack. Moreover, Liu Bei gathered a large number of talents and Zhuge Liang supported him, so he became a relatively powerful force at that time, and Cao Cao could not win him in a short time.
Although Wu is weak, its naval combat capability is very high, and the Yangtze River is their natural barrier, so it is impossible for Wei to send troops to attack. Battle of Red Cliffs made Cao Cao more injured and had to occupy the north, so it was also a helpless move at that time. It was not that Cao Cao wanted to recuperate like this.
Moreover, the tripartite confrontation does not mean that Cao can break it only by a few years' practice, but it takes a long time to gather strength and break this situation in one fell swoop. Moreover, Cao Cao himself died prematurely because of some of his own diseases, so it is difficult to achieve such a goal.