Because "AGI" is very poorly defined, and ChatGPT is very "general" (compared to everything before it) and matches some (but not all) definitions of "intelligent".

Because drumming up talk about AGI is a really great way to get funding for your startup. The tech industry sustains itself on hype.

Not only but also.

Because transformers et al have gotten us the closest we've ever been to any system that can even claim to be AGI.

First make it work; then make it efficient.

... seems potentially better than the other way around? Well, I suppose it depends.