Moreover, the GPUs and more so, DSPs and ISPs in your phone or PC are hidden from you in that they run code written by a very small number of people. You don't even have an idea how many small DSP cores are scattered throughout a desktop-class chip, let alone what they do or how to program them. Effectively it's for internal use of a very small number of hardware and software vendors, and the software is very much tied to the hardware.
The reason computing hardware used to be open is that very few could make it and they only stood to gain from making it usable in as many applications as possible, or at least so they thought. Once (almost-)cloning hardware products became increasingly cheap with less and less vertically intergated hardware vendors (from fab to design), vertical integration moved to design+software because that's how you fend off competition today.