Tim Miller recently decided against directing Deadpool 2 due to creative differences with star Ryan Reynolds. However, with screenwriters Paul Wernick and Rhett Reese set to return, most of us assumed that the ramifications of that wouldn't stretch beyond a new filmmaker being at the helm of the follow-up. Well, one more person now isn't returning, and that's composer Junkie XL. He makes the reasons for that clear below, and it obviously stems solely from Miller's decision to walk away. 
 

It is with a heavy heart that I have decided not to score the upcoming Deadpool Movie. I love this character and creating his and the movie’s original score was a monumental chapter in my life, personally and professionally.

Since it was revealed that Deadpool’s brilliant creative director Tim Miller will not be involved in the project anymore, I have undertaken some soul searching. Tim was the driving force behind Deadpool and me getting involved in this amazing project. Deadpool without Tim at the
Source: COMIC BOOK MOVIES