From what I remember, the "creators" of Grievous originally had this idea... to make General Grievous be the resurrected Darth Maul. Their idea was that Sidious "saved" Maul much in the same way he does Anakin as Vader. In fact, that is why Grievous shares the same looking eyes.
When the character designers (artists) pitched the idea to Lucas he said emphatically "NO".
I guess it is just another case of the FanBoys getting pushed down by the man.
If you think about it, this would have made a lot of sense considering that Anakin was made to live through the use of a mostly mechanical body so seeing Maul "living" the same way would have made sense... but then again, we are talking about the prequels so such nonsense as "making sense" just goes out the window
