In his past life, Amon had punished people for slight offenses, much less an attempt for his life. However, it didn't mean he was a maniac who would get back at people for whatever small violation they did to him. If he was such a person, he wouldn't have the time to do anything else because he would have to kill everyone.
He was never a person controlled by emotion or grudge. He simply took the chance if the opportunity presented itself, like the time with Wei Feng. If not, he wouldn't force himself to take revenge. The same thing could be said with his current situation. He did investigate and learned about Lin Zuyi's two attempts on his life, but he never did anything about it. If Pai Kuan didn't come knocking, he probably would just leave the matter to a later time when he could destroy the Lin clan with ease. But since Pai Kuan did, he figured he would just use it as a chance to settle these old grudges.
