Why does Athena send Telemachos off to visit Nestor and Menelaos, instead of simply telling him that his father is almost home?

Telemachus must go through some test of becoming a man and he must complete his quest for his father to demonstrate that he can be the kind of hero his father would have raised him to be. He learns what he needs to motivate him to return home and then be a wonderful support for his father when Odysseus finally does return.