Board Thread:Theories and Speculation/@comment-25132842-20180405032134/@comment-26107879-20180407020715

If you are asking why Kakashi does not have EMS, it's because just transplanting is not the only thing needed. Look at Obito and Madara. Both had transplanted their eyes into one another and no Eternal Mangekyo of their own transpired. Kakashi went as far as having both eyes and still did not awaken an Eternal Mangekyo. You need 3 things. Transplant. Both having Mangekyo. And finally, a strong blood tie, ideally a sibling. Without those, you just get a transplanted Sharingan such as what happened with Madara with Obito's Mangekyo.