Via Honest Wagner, the Staten Island Advance reports that the Pirates want to shed salary:
That the Pirates tried to attach Burnitz to Hernandez is not hard to believe, since it has been reported (via Where's Van Slyke?) that the Bucs tried to do the same thing in discussions about Craig Wilson.
I certainly wouldn't mind if the Bucs traded Burnitz, but if it's true that they're trying to attach him to Wilson and Hernandez, they're not making good baseball decisions. Burnitz probably has negative trade value right now because of his performance and salary, so by attaching him to players like Wilson and Hernandez would seem to legitimately have trade value, they reduce what they can get for those players.
Relatedly, check out this excellent post by Van Slyke about Littlefield's trading skills, or lack thereof.