Because all of what you refer to as "dumb AI" is actually machine learning algorithms trained for very specific pattern matching. They are approaching abilities of the human brain such as pattern matching in vision, hearing and language (which if you think of it probably evolved from a common system).

What seems to be constantly overlooked when discussing AGI is that we as a species still do not have a reasonable comprehension of how the rest of the brain works.

I would like to ask you, why do you think a bunch of eyballs and ears would somehow be able to end up as intelligent?