Things that Make Me Go "Why?"

In this day and age, if you spend lots of money and reasearch work to produce a fancy several-hour TV special with tons of special effects, why would you NOT sell the DVD?

There's several things in that category, but the one that perhaps puzzles me the MOST is National Geographic's "Extraterrestrial" special. I find it incomprehensible that they haven't yet released this quite interesting speculative special on DVD. It would seem to be a no-brainer -- make special, sell DVDs. The longer you wait, the LESS you sell, in general.