Why did Yang Yi decide to leave the incoming reinforcements and go off alone?
The reason is simple: Yang Yi is not just an enemy of the clean-up crew; he's a deadly enemy, the type where if Yang Yi doesn't die, the clean-up crew will be finished.
Yang Yi is still holding onto the revelation. What is this? It's the lifeblood of the clean-up crew, a treasure longed for by the Grey-cloaked People. So even ignoring the fact that Yang Yi killed Kant and Bruno, the clean-up crew has to catch him, kill him, and seize back the revelation.
As for the Grey-cloaked People, unquestionably, their desire to kill Yang Yi and snatch the revelation is just as strong if not stronger than the clean-up crew's.
No matter how many people accompany Yang Yi now, it's useless because he can never match the number of the clean-up crew and definitely cannot surpass the strength of the Grey-cloaked People.
But it's different if Yang Yi leads the people away.