Why did Lu Shang become a vassal of Qi?

King Wen died and his son King Wu succeeded to the throne. King Wu still attached great importance to Lu Shang, calling him "the teacher is still the father". In the fourth year of King Wu's accession to the throne, eight hundred vassals joined forces with Jin Meng, with Lu Shang as the commander-in-chief. The scale of this exercise is huge and inspiring. Everyone thinks that business can be destroyed in one fell swoop, but Lu Shang and Wu Wang think that the time is not yet ripe. Two years later, King Wu decided to cut down on businessmen, and the result of divination was unfavorable. At that time, it was stormy, and civil servants and military commanders all thought that sending troops at this time was against God's will, but Lu Shang urged King Wu to send troops to attack. So he decided to attack Zhou, and he won at once. After the war, King Wu rewarded people with meritorious service, and Lu Shang made the greatest contribution, making him a vassal of Qi in Yingqiu (now Linzi North, Zibo City, Shandong Province).