Well because if you listen to his interviews, or read what Regal or Trips and others say about him i don't think he's a yes man.
Also he doesn't do main roster house shows. He's done the two recent european tours, the Australian tour and the Asia tour. It's obvious why he was put on those tours. The only thing he's done for the main roster is a dark match at a Smackdown taping and a some special live shows, where he was against other NXT roster members anyway. Other than that he's been touring with NXT for the last year.
http://www.profightdb.com/wrestlers/finn-balor-3023.html Dunno where you got info he skips NXT shows for WWE?...
Ofcourse he wants to be on Raw and Wrestlemania, but again i think he also knows if he stays in NXT as it gets bigger, his name gets bigger and it'll be harder for them to not give him a big push right out the bat. Why jump from NXT, when it's the fastest growing brand in Wrestling at the moment, do get stuck in the shuffle?
As i said, we don't know what they'll do with the Bullet Club, i think it could get a refresh in America. Balor is trusted and is listened to creatively. I think it's going to be used to get Balor onto the main roster and in the upper to upper mid card straight off the bat.
You never said who else is coming to WWE?..