Because so many people think, errantly, that the Buddha's teachings are all about karma and reincarnation. And they are constantly being told, errantly, that the Buddha's teachings are all about karma and reincarnation by monks who think, errantly, that the Buddha's teachings are all about karma and reincarnation, because they have been told, errantly, that the Buddha's teachings are all about karma and reincarnation. If they aren't shown otherwise, how are they going to discover the truth?
The Buddha's teaching of Anatta is not "There is no self".