Actually, while he was good in coverage, he was suspect at tackling/defending hte run. Given that he's built to play ILB, where run-support is primarily needed, secondarily to covering receivers, it's pretty obvious why he's no longer here.
I mean, it's a preety telling indictment of your skills when one year you're replaced by an againd Zack Thomas, and the next year, when he leaves, your position is bolstered by Brooking, another older LB. But what htese veterans can still do, even with their diminishing skills, is still cover the running game better than Burnett.
So Burnett is wrong to say he had no chance to showcase his skills; in fact, he had a chance, but only he didn't showcase the ones he needed to when callrd upon. And instead of spending the little free time he had to improve them, he instead spent that time contributiong to the DMN blog. That tells you where his "I'm not accountable" attitude comes from.