Board Thread:Wiki Discussions/@comment-3238846-20140422105553/@comment-28861328-20140427230225

Yonbi notes in a canon flashback, back when Naruto talked to all the beasts in his subconscious, that he and Roshi weren't on good terms. Even Roshi admits to this. So it make sense that Roshi would have to go on a "journey" to gain power that Naruto can simply ask for, in the same manner that Naruto had to go through all that training with Jiraiya to force Kurama to give him chakra before they became friends and he could ask for it.