How do you know that was Lucas and not Filoni who brought Maul back? (may have been Lucas, but Filoni had far more control over the cartoon if I recall, and Ahsoka...his pet...was more a pure Filoni thing than a Lucas thing, along with many of the other introduced characters of the cartoon).
Lucas is given far more credit on the Clone Wars than he actually probably deserves, and far less credit on the later portion of the EU novels (Legacy of the Force and the later portion of the New Jedi Order series) than he also deserves.
Neither of which were really A-class Canon (or whatever it is called today...G class...L Class) at the time (which were basically just the movies, the books that based themselves on the movies, and the Radio Dramas).
They both were a step below that, both had Lucas involved...but not so in depth that they were considered as official as his stuff that he was truly over, and were not entirely controlled in as much detail as his own Canon. I think many put the Clone Wars above the EU novels...but both were not entirely Lucas's creations so not his actual universe (but considered an alternate universe he approved and was fine with,,,unlike the Disney one that came after which would fall in line with F Canon...aka...Fandom Canon).