Because deep down, it's not what they do. They are optics and camera hardware companies. In the race between physics and software, they are on the physics side. This is evident in the entire user experience. They keep missing the boat with the way people actually use photography today, and don't even seem to care much. There's not much evidence they have the kind of research expertise that Apple, Google or Adobe built in signal processing and image processing, either.

See also https://www.dslrbodies.com/newsviews/news-archives/nikon-201... and https://www.dslrbodies.com/newsviews/news-archives/nikon-201...