When my earliest extant source for Alexander the Great tells me that he is relying on contemporary biographers of Alexander, I take that as some evidence that information about a historical person was remembered and passed on. I may need to consider the possibility of invention or falsehood, but it is at least some evidence.
On the other hand, when my earliest extant source for Jesus tells me that he is relying on divine revelation, supernatural appearances, and centuries-old holy writings, I do not think that I can take that as any evidence that information about a historical person was remembered and passed on. I can consider the possibility that this occurred, but I cannot say that he has given me any evidence that it did. Moreover, I may even need to ask whether he hasn't given me some evidence that the opposite is the case.