Because intelligence as a single-dimensioned parameter is a myth.
We already of have software with super-human information processing capabilities; and we're constantly adding more kinds of software that outperforms humans in specific tasks. Ultimately we'll have AIs that are as versatile has humans too. But "just as versatile" doesn't mean "good at the same things".
So it's probably true that software is getting smarter at exponential rates (and humans aren't getting smarter as far as I can see), but only in certain ways.