Although I agree with you saying that Discovery wings repeats many shows, it is not the only channel to do so...
It seems the Discovery Channel "s" are running out of things to document and air onto TV. A possible reason for this could be the shear amount of documentary channels talking, almost, about the same things.
How many shows have I seen about Tornados?...not the aircraft, the spinning cloud things. I should think we could re-write the scripts to some of these shows we see them so many times...unless we have the intent and/or effort of reaching for that control and pressing a number on it
Smooth skies