Former drummer of Dream Theater and Avenged Sevenfold, Mike Portnoy spoke in an interview with Metal Wani and explained why he leave Avenged Sevenfold. He said (transcriped by Blabbermouth):
“I love the album and I love Brooks. I’ve always been a fan of Brooks, for many, many years — whether it be the INFECTIOUS GROOVES stuff, or even recently, he did an album called FARMIKOS [the Los Angeles-based band featuring former OZZY OSBOURNE and DAVID LEE ROTH guitarist Joe Holmes], which I loved.
I’ve always been a fan of his drumming and I think he’s the perfect fit for those guys.
I think when I was playing with them, they just weren’t ready to commit yet, and I think with me came too much history and focus, so I understand why, after my commitment for the year was over, that they wanted more of an unknown drummer with Arin; I get that, I totally understand that.
And then, for whatever reason, that didn’t work out and they went with Brooks is their business and their story. But I love where they’re at now, and I’m happy for the level of success that they’ve had.”
You can watch entire interview from below.