I'm likely very wrong but this would be some of my thoughts on the whole Rock situation and why he didn't show:
A) Doesn't want to be involved to over-shadow Cena's record breaking achievement.
B) Stayed behind as just having him turn up every Wrestlemania will get stale and, as a lot of people already do, expect him to turn up anyway.
C) The storyline will continue, likely tonight on RAW and he will introduce the Corporate champion and how he has Cena's soul.
D) Other commitments - highly unlikely as this man must be booked up for at least 18 months in advance.
E) They are dropping the whole involvement of him as it was just a plot device to turn Cena heel and introduce (poorly) Travis Scott.
I re-watched the main event and really feel for Cody and how feeble and soft they made him. Comparing this match to the epic match with Reigns last year is night and day. I've got no problems with Cena winning a 17th but i shudder to watch him wrestle again. He can't carry anyone anymore and is just a liability in the ring at the moment.