But flying machines are well defined, or at least it's easily possible to come up with a good definition. 'A machine capable of transporting a person from a to b without touching the ground at any point in between', or whatever.
For AGI, that's very far from being true.
People did genuinely struggle to define "useful flying machine", which is why you see the description of the Wright Brother's flight come with so much detail: "first controlled, sustained flight of a powered airplane".
Well there are paper darts and weather balloons but most people were interested in a powered machine to transport people. Likewise with AGI but I'm guessing most people are thinking of something that can do what people do?