Don Rosa worked with the various comics publishers, not directly with Disney. This one was published by Egmont (in Denmark). As a result the comics writers actually have a pretty high degree of creative freedom, compared to people in other parts of the Disney empire.

Though he did decide to retire, partly for health reasons, partly because while everyone feted him like a rockstar when he was visiting Europe, he certainly wasn’t paid like a rockstar by Disney. (…or, given how little money flows toward music artists these days too, maybe he was paid like a rockstar.)