Board Thread:Theories and Speculation/@comment-35172651-20180401134411/@comment-26107879-20180407021459

Probably because Obito's Chakra was mutated. Like Kabuto who was corrupted with many forms of DNA thus his Chakra was, Obito was corrupted with Hashirama's DNA. Then you also had Obito wearing Tobi the entire time. The mixture of Chakra signatures would prevent a Byakugan user from recognizing Obito's none corrupted Chakra implanted into Kakashi.