Vince will do what Vince whats. Vince wanted Reigns vs Undertaker, we got Reigns vs Undertaker. That leaves Cena without a match, so the proposal moved to Wrestlemania.
Only thing I don't get is how Styles-Orton did not happen. Wyatt vs Orton could have ended at EC. I guess the McMahons have to much ego, so a Shane match was going to happen anyways. So bring in AJ Styles in order to carry Shane into an entertaining match. Who else would do it? Ambrose or Wyatt?
Vince's selfishness cost him the greatest Mania of all time. Not that the end result was bad, but it could have been 10 times better.