I'm guessing because of the logistics and everything, and I think I mentioned this earlier... but this was the first Wrestlemania I can remember in a long time where Vince didn't have a part in the show at all - no announcing, match, or angle.
As for Wrestlemania returning to Orlando... why do you think the Super Bowl returns to the same cities each year? Those cities know how to host an event, and by all indications, Orlando went all out for this one. The WWE has been nothing but positive in terms of what the city and its management did in relation to landing and hosting the event.