The former Hammers captain left the club by mutual consent in the summer after spending four years in East London.
He told Sky Sports' Goals on Sunday: "It was a wrench to leave West Ham, but it was the right time.
"Slaven was brilliant when he came in and we got on really well. He was honest and we just came to the agreement that it would probably be best if I moved on.
"He said 'you're not guaranteed a place', which I've never had in my entire career, contrary to what people think, when I played under Sam. But he was wanting to bring in a lot of midfielders, which would have put me back a bit more.
"I've come to the decision that I'm not going to play as much and I don't want to just sit there and earn my money. For the majority of my career I've played every week and last year, sitting on the bench didn't really suit me.
"I was very miserable at home, the wife will probably tell you, so it came to the point this year, I thought I'm not going to play as much as I would have liked.
"I've had four fantastic years. I've got some great mates there that I'll have for life, but I want to go to a new chapter and contribute to a new beginning of something. I want to be a part of that and achieve something again."