Ask HN: Why do some hardware only have proprietary drivers?

Inspired by nerdponx: https://news.ycombinator.com/item?id=14050297 During all my years running linux I have only encountered binary, proprietary, driver blobs for some certain type of hardware. Most commonly graphics cards and wifi-adapters. Why are just those drivers closed source, and not all? Is it that other stuff, like USB-controllers, are standardised in grater extent and therefore opensource reverse engineering efforts can be focused and deliver open drivers? Or do the manufacturers actually provide open drivers? If they actually do provide them, why do they? Or perhaps rather, why does not AMD/Nvidia do it? In the case of binary blobs in mobile devices, I have read stuff about security aspects of keeping the baseband drivers closed source. Something about protecting the cellular network. Is there anything behind this?