Because that’s how AGI is defined. https://en.wikipedia.org/wiki/Artificial_general_intelligenc...: “Artificial general intelligence (AGI)—sometimes called human‑level intelligence AI—is a type of artificial intelligence that would match or surpass human capabilities across virtually all cognitive tasks”
But yes, you’re right that software needs not be AGI to be useful. Artificial narrow intelligence or weak AI (https://en.wikipedia.org/wiki/Weak_artificial_intelligence) can be extremely useful, even something as narrow as a services that transcribes speech and can’t do anything else.