I cannot say for sure but I got the impression that it went out of print because they had many problems with the sets. I remember reading about it (I think it was on this forum but I could be mistaken) and it can also be seen in some of the Amazon reviews. While they did seem to fix the issues it seemed like by the time they did they just decided to throw in the towel. Once again, I could be (and probably am) wrong about the reasons but that has always been my impression.Timothy:
I'm not sure why Season 6 went out of print. It was originally a MOD DVD-R release from Universal which they then quietly switched to pressed disc release.