It’s not that Dorgon was not the emperor, but that the time was not ripe.

Dorgon has always had the ambition to proclaim himself emperor. The main reason why he did not proclaim himself emperor was because he believed that the time was not mature enough and he did not dare to act rashly. But all his actions are taking him one step closer to the emperor's throne. At the same time, Dorgon was less than forty years old at the time, so he certainly thought he still had a lot of time.

In the end, Dorgon’s life was fixed at the age of thirty-nine. He was only one step away from the throne of emperor many times in his life, but in the end he failed to realize his dream. Apart from helplessly complaining about his bad life, there seems to be no more appropriate reason to explain why Dorgon failed to become emperor.

Extended information:?

The first time Dorgon had the opportunity to have "close contact" with the throne was when Nurhaci died. Dorgon was only fifteen years old at the time. Judging from the various arrangements made by Nurhachi during his lifetime, it is likely that he decided to leave the throne to Dorgon. For example, he handed over most of the Zhenghuang Banner and Xianghuang Banner that he commanded among the Eight Banners to Dorgon and his two other half-brothers Azig and Duduo, and made it clear that Azig would serve as the Banner after his death. As the leader of the Yellow Banner, Duduo served as the leader of the Zhenghuang Banner and gave another flag to Dorgon.

The second time Dorgon had the opportunity to ascend to the throne was when Huang Taiji died. Since Huang Taiji had not designated an heir during his lifetime, all forces coveted the throne. At that time, Dorgon was already a powerful figure in the Qing Dynasty. With his outstanding achievements, many Manchu clans supported him in proclaiming himself emperor. Dorgon's main competitor is Huang Taiji's eldest son Hauge. From a legal perspective, he has an advantage over Dorgon. At the same time, the forces supporting Hauge are no less than Dorgon.

Dorgon's third chance to become emperor was naturally after he gained power. At that time, Dorgon was the only one in the civil and military dynasties who followed Dorgon's lead, and the young emperor Shunzhi was even more obedient to Dorgon. At that time, when Dorgon went out to hunt or lead troops on an expedition, the princes and nobles would kneel down to see him off. Dorgon also began to imitate the emperor in ceremonial arrangements, "the ceremonial guards, music, and bodyguards used were all imitating the supreme." In all government affairs, Dorgon no longer asked humbly for instructions. He did not follow the emperor's orders, but always issued orders, just like the emperor.

Reference: Baidu Encyclopedia—Dorgon