Why wasn't Donald Duck in the original DuckTales?

In the video linked above, Seaniccus explains why Donald Duck got ditched in favor of Scrooge in the 80s version of Ducktales.

Who's never wrong but always right? Who'd never dream of starting a fight? Who gets stuck with all the bad luck? No one, but (a carefully rebooted) Donald Duck.

I've always had a special place for the Disney ducks in my heart. Unlike his rivals at different animation studios—Bugs Bunny, Felix the Cat, and Woody Woodpecker—Mickey Mouse always seemed devoid of humor or personality to me. Bugs was a trickster with caustic wit and a gift for impersonation, whereas Mickey was just a milquetoast. The ducks, on the other hand? They're loaded with personality and humorous character quirks, and none more so than Scrooge McDuck. Although most remember Scrooge for his starring role in the 80s cartoon Ducktales, many fans don't know that Donald Duck used to be the anchor for the franchise. 

Mickey Mouse should be retired; Scrooge McDuck needs to be Disney's new mascot.