Board Thread:Theories and Speculation/@comment-27717552-20160513151229/@comment-734582-20160518140753

GreatestSin wrote: ^and dont forget that rasenshuriken only was spammable for naruto because of his big chakra reserves which got boosted even more by kurama...

otherwise 2 or 3 (in sage mode) would be his limit... Jiraiya at least has significant enough reserves to do it, since he can do sage mode.

However, Jiraiya spent most of his adult life as a spy for Konoha, by keeping tabs on Orochimaru and later on Akatsuki. during this time he mostly specialized in infiltration (as his various spacetime techniques show). Even someone like Itachi preferred not to fight him, and Itachi was clearly one of the stronger of Akatsuki.

So simply, there was no immediate need for Jiraiya to become stronger (unlike Naruto). The Sannin truly were shinobi above most other shinobi. it's only the relatively recent emerging of strong shinobi and the combination of bodyhacks that created ninja beyond them.

Even Orochimaru didn't spend time becoming stronger. He simply gathered information and made experiments, but most of that was geared towards regaining his old strength. The Sannin simply spent their adult lives gathering info: Tsunade resumed her medical studies, Jiraiya spied and Orochimaru experimented.