Most likely because it interfered with and suggested going against Japanese tradition...
Explanation:
Some people hesitate letting in new religions or events into their culture because they're worried about the effects it will have on them and their traditions and if any will be replaced by new ones they dislike.
Buddhism entered Japan through Korea. They aimed to fulfill the diplomatic mission that included images and many other activities. Buddhism, therefore, as a religion, offered spiritual transcends that conquered the suffering that existed. The circle of birth continuous together with deaths and thus led to continuity of karma and other consequences that affected many lives during the century. Therefore, these total actions, both bad and good, occurred in the region during that time.
