Board Thread:Theories and Speculation/@comment-3001903-20160813043039/@comment-2120712-20160912061120

Probably because Kishi didn't want Tsunade to be a carbon copy of Hashi not to mention her having wood release would mean that the Nine-Tails attack on Kohona could of been ended with less blood being spilled(then again if the Uchiha were not quarantined then they could of overrode the genjutsu controlling him.)

In universe wise, prior to her fame with medical ninjutsu, Tsunade's claim to fame was her grandfather, so that would probably be motivation to develop her own skills or at least skills that had nothing to do with Hashi, and if she does have WR its probably under powerful seals, maybe to prevent enemy nations targeting her for such a ability.

Personally I think the KKG is just extremely rare. Had Tsunade had kids, I have no doubt one of her descendants would have shown up with WR but we will never know unless during the timeskip she found another man to love and she hasn't gone through that yet(which is possible because my grandmother never went through it)