Contrary to belief, Itachi was not entirely unaware that he had massacred his clan. He knew there would come a time when he would have to atone for his sins. Itachi still valued control over everything else; if he had to atone, then he would do it his own way. He would twist fate so that it unraveled in his favor.
Itachi hadn't wanted to be understood, it wasn't what he needed. No, he needed to be punished. But no one was strong enough. But someone could be.
He would have asked Kakashi but deep down, Itachi knew he could not. No, it could not be Kakashi. Either Kakashi would not understand or, and Itachi feared this most of all, he would understand all too well. Kakashi might have used his own Sharingan, could have seen the truth.
But there was one person in the world who could come close to understanding. Close being the key wood. One person who would follow him to the ends of the world, if only to appease him. And that one person was Sasuke Uchiha.