Mainly caused by multiple vendor implementations and a large variety of media types. Although cdrkit has trundled along I'm not surprised it's not getting the attention of other more sexy projects. The work is generally boring and requires having a large number of different vendors hardware to test well.
Having said all that and as others have pointed out I can't actually recall the last time I needed to burn a CD. I certainly have two very dusty spindles of CDs and DVDs in my office.