Rashi writes that Kaleiv broke away from the meraglim and stopped off in Chevron in order to daven at the kever of the Avos and elicit their zechus. Where was Yehoshua? Why didn't he join Kaleiv there?
My wife suggested that Yehoshua didn't need to join him because Yehoshua had Moshe Rabeinu, a living rebbe of the highest rank. He didn't need to go to kevarim to connect with the mesorah of the past; he had a living connection to it in the present.
I would just add that this fits perfectly with the Maharal in Gur Aryeh who writes that Moshe changed Yehoshua's name and davened on his behalf more than he did for anyone else (the implication of Maharal, as R' Hartman points out, is that Moshe did daven for everyone, just not to the same degree) because Yehoshua was his talmid. If a talmid fails, it reflects back on the rebbe; when a talmid fails, it is as if the rebbe has suffered a personal failure. That special bond existed only between Moshe and Yehoshua.