Everything we see is an illusion. We don’t think about it that way, but what we see is a fiction created in our brains based on the information our optic nerves supply it with. Fiction can be true, though, and we expect it to be true even if we know it’s not real. Abstraction of reality is something humans love deeply.
Someone paid $90 million for a David Hockney painting, a self portrait. And you could, if you liked, simply go get a photograph of Hockney instead, posed in the same way. But in the fiction of art we expect to find something reality alone can’t provide.