Why didn't Cao Cao use rockets to shoot arrows by borrowing grass boats?

There were rockets during the Three Kingdoms period. A rocket actually soaks oil in an arrow and burns it. Rockets are very useful for Kong Ming's straw boat. Grass man, green cloth, and see if the boat is a wooden boat. If the intensive rocket rain hits the boat, I'm sure it will be like burning the boat. Coupled with the strong wind, Kong Ming is afraid of born to die. At that time, the rocket seemed to have come out.

Many people say that Cao Cao didn't know the truth and didn't use rockets. So since you dare to use arrows to resist enemy ships, there may not be armored ships at that time, and even if there were, I don't know what effect bamboo arrows will have. The straw boat came from the wind. If it is burning, it may burn Cao Cao's Dazhai together. But if the burning boat really pounces on Dazhai, he can use bamboo, with iron wrapped in the front, to resist the grass boat and keep it away.

Based on all the reasons, Kong Ming made a major mistake, which should have been caught by Cao Cao and wiped out in one fell swoop. But Cao Cao didn't. He just hurriedly resisted, didn't see through the flaw, but helped Kong Ming.