Board Thread:Naruto Discussions/@comment-24531362-20140723084127/@comment-24531362-20140729101624

Jashin Uchiha wrote: He has seen Kakashi using it, he could have tried to copy Kakshis version before but it didn't work, now that he has both eyes it works.

Just a guess.

If by copy you mean Sharingan copy, there are two problems. 1. Kamui is a Kekkei Genkai ability, which the sharingan cannot copy. 2. Obito lacks the individual skill to execute the Kamui variant expertly, just like Sasuke couldn't do the Primary Lotus after copying it because he lacked Lee's physical prowess in Part 1. If you just meant basic imitation, problem 2 still applies.