Because the people who are qualified and skilled enough to make one from scratch are working for companies like Qualcomm, 55 hours a week at a salary like $190k.

It's kind of like asking where there aren't any gpl licensed m.2 ssd flash controllers, the people who design them are getting paid nicely to design and sell a commercial product. It would be cool if there were such a thing, but there is only so much "free" expertise to go around...