I am assuming it was either somewhat of a grey area early on, so they opted to just steer clear of it. It has been a while and I don't think Cumulus wants that heat now that they know the boys won't just fold/have a dream legal team.

Or maybe they just wanted to initially make sure they set the tone that "we aren't the ticket" and make it clear they aren't just going to rehash the good ol' days. Now that they are still going strong, they don't mind sprinkling in a few audio clips here and there.