Board Thread:Theories and Speculation/@comment-26889573-20151008053113/@comment-734582-20151019110620

AsianReaper wrote: @Slug Princess00, Orochimaru didn't get sage mode. My guess is that Tsunade left the shinobi life before she leaned sage mode. I think it's a combination of two things. First off, Tsunade was attempting to emulate Hashirama's power, which Sage Mode can't do. Strength of a Hundred seal can. Secondly, she seems to have been wandering (like Jiraiya) for a very long time, so i think she never took the time to learn it. Thirdly, unlike Jiraiya who dreamed of power (to show his worth) and Orochimaru who dreamed of all jutsu, Tsunade dreamed of saving people (and thus creating medical-style jutsu) and therefore Sage Mode didn't fit her bill.

Lastly, it's possible that the nature of the Strength of a Hundred Seal makes balancing nature energy that much more difficult since it's a mass of chakra that suddenly activates, meaning you'd have to be pretty good at on-the-fly ratio adaption.