Why was Don Pasquale difficult for its performers despite its comic mood?

While Don Pasquale is a buoyant and delightful opera buffa for the audience, it is considered a formidable challenge for its performers due to its demanding vocal and dramatic requirements.1

Although Gaetano Donizetti composed the work quickly, he specifically handpicked the cast from the most famous singers of the day. Because he had worked with these performers previously and understood their specific vocal and dramatic capabilities, he intentionally entrusted them with highly challenging material. This complex vocal writing is a hallmark of the work, requiring significant skill to execute despite the lighthearted and comic nature of the plot.1