So I've listened to a few of these interviews with Punk, because I've always found him a compelling interview subject and personality in general. But after listening to a few interviews since he joined the UFC, I figured something out: he's not an entertaining interview subject outside of the WWE.
People gravitated towards Punk during his wrestling days because he was outspoken, unafraid to express a strong opinion and didn't always tow the company line. He didn't mince his words and had a way of cutting through the bullshit. That's what made him likable.
Every interview I've heard with him since he joined UFC (except for the Cabana podcasts), he's talked on and on while actually saying very little. His interviews are full of meaningless platitudes and non-opinions. He almost never gives a straight answer to any question. Maybe he feels he has to pay his dues more before he can become outspoken about the UFC, but it really isn't what I would have expected from Punk a year ago.
Maybe he's only entertaining when he's not happy.