What are you talking about. WWE has been in a "lull period" since after WrestleMania 28. He could've been debuted in May or any other month after WrestleMania because there isn't anything huge going on right now or since after WM.
The 1000th episode of Raw?
Have you been living under a rock? WWE especially hyped the 1000th episode for months on end. I said he could have debuted after Mania IF his feud w/ Foley would have stuck, but it didn't. Ambrose would have been lost in all that build up, no matter how good he is.