It would take a lot of time and money to create anything competetive with Nvidia and AMD's offerings. It took Intel over a decade and their dGPUs still aren't very good.

GPUs are insanely complex and the drivers are full of hacks (even per game basis, a driver could swap shaders with ones written by Nvidia/AMD if it detects you're playing the newest popular title). The threshold to enter the market is incredibly high.