Because 50's era scifi is cool, while 90's era superhero anime regurgitated bullshit is not. You can polish a turd and make it look like bugs bunny, but it's still a turd.
Erm, that is to say the Loonatics team hadn't seen one. Duck Dodgers was actually the best thing that's been done with these characters since about the 70's.
There's like four different theories contained in these comments about who made this theme song. I'm gonna go on record as saying it was Devo. Guys, Devo did it. Devo. They're a band, right? The song was pretty good, and almost made me believe that Duck Dodgers could work for more than four minutes at a stretch.