See his blog post here.
Specifically, he comments that:
"It's going to sound cliche' but the truth is, at least for myself , I chose to leave. I approached Matt Idelson about 4 months ago right after we finished War of the Superman and let him know I wanted to move on.
wo years on a series as an artist is a long time creatively, and like any artist, you feel the need to stretch and do new things.
There was no malice, no secret agenda on DC's part. There were discussions of what I may do next but nothing finalized, including Birds of Prey."
I'm sad he chose to leave, but very gald he wasn't pushed out. After all the rumours about Igle moving to BoP it occured to me that leaked info like that can have a negative impact on a person's career. So, I'm glad that that isn't what has happened here.
I'm also *so* relieved that Igle and Benes aren't simply swapping books. can you imagine a modenr Benes on a Sterling Gates written Supergirl? The mind boggles.