WrestleMania 35: 5 biggest reasons Vince McMahon didn't book Dean Ambrose 

#3 WWE doesn't have an ideal opponent for Dean Ambrose

WWE could have booked Ambrose against Drew McIntyre

Let's say that time is not an issue for WWE. They can add a couple of more matches to the show. But what would they do if there isn't an ideal opponent for a Superstar? The answer is simple, that wrestler won't get a match. It has happened before and could be the case with Dean Ambrose too. Almost every big Superstar is going to perform at WrestleMania, and only a few of them are not yet booked for the show. From Roman reigns to Seth Rollins, Brock Lesnar to Ronda Rousey and Drew McIntyre to Bobby Lashley, everyone is busy with their own storylines.

So there aren't many opponents left for Ambrose at the show, which could be a reason why he doesn't have a match at WrestleMania. However, this may not be entirely applicable as some top Superstars are still available to perform at the show.