That's why I say it is enigmatic. It doesn't make sense and only seems to be a plot device. Not as bad as the sharingan because it is not as abused, but still just as plot convenient.
Why can't wood release be passed down familiarly? Why can't Tsunade do wood release?
By the way, yes Sakura has earth and water I do believe, but she never uses them. Hell, Naruto never uses his wind release other than rasenshurikan.
I get Wood Style is a nature transformation Kekkei Genkai, but you said it, James! Why couldn't more depth go into those kind of Kekkei Genkai to make them make sense? Same with Kekkei Tota like Onoki's Particle Style!