Board Thread:Episode Discussions/@comment-1018594-20150212111605/@comment-1512913-20150214130733

Lee can use pure chakra, he simply can't do nature transformation. He doesn't even have a chakra affinity, he has no inborn talent in regards to chakra manipulation. If I were to guess, Lee comes from a line of non-shinobi, hence he has no genetic predisposition for that stuff, he is a first ninja in their family or so.