when Mitch's brother was ill with cancer he secluded himself from others and didnt want to see his family including Mitch. Mitch didnt ever have a chance to really talk to him or see him while he was dying and Mitch regrets it. Now with Morrie MItch can actually talk to him and help him through it and he wont loose contact so he has nothing to feel guilty about.

 It helps Morrie to detach himself from his dying experience because no one wants to remember all the time that they are dying. They already feel it because their body is sick and Morrie wants to forget about it. I would feel the same way.