I suppose it's a little story you're reading. 这其中的原因，我也不知道。in this sentence, I don't really know what the author was trying to express either, because he had already told us of the reason in context. The reason is obviously the history traditon mentioned above. Then why he said 'the reasons of this, I don't really know', I can't find his intention. But I'm sure this sentence is not very important in understanding the whole story, so I suggest you do't worry about it.