Maybe he's a busy guy, the universe is a big place.
"Ok, so I have to make a second coming on Omicron Persei 8 tomorrow, a third coming on Uranus, and another 2nd coming on Hovering Squid World 97A. Oh, shoot I forgot about Earth again. Sorry Mr. Russel! I'll pencil you guys in later... 1975 sound good for you?" 1975 comes along.... "Shoot forgot again! Why didn't you remind me Mr. Russel? Mr. Russel?... Oh right, that mortality thing, I forgot about that. Well, I get to Earth some time later."