Board Thread:Theories and Speculation/@comment-33959444-20180610211826/@comment-33959444-20180616193731

AsianReaper It did take effort controlling the Bijuu, but Obito showed no noticeable signs of strain. So, it couldn't have been that bad that it prevented him from analyzing his opponents' abilities.

And magicians normally try to actually do something in order to take the audience's attention away from the other hand. Over here, Naruto's Kage Bunshin was charging straight at Obito. There was nothing "camouflaging" it from Obito's eye so that he wouldn't see Kamui. If he saw a Rasengan disappearing, it'd only make sense he'd see the Shadow Clone disappearing.