Reads like Intel will be using Nvidia's stuff for integrated systems, and doesn't say anything at all about discrete graphics cards.

If you're integrating a GPU, then it's going to be either for a laptop, in which case performance-per-watt and total die size are very important, or it's for a generic business PC, in which case 'as cheap as they can get away with' takes over. A B580 might be the best mid-range graphics card, but those aren't the areas where it shines. Using someone else's tech makes sense.