Look up Project Ada, I believe it was. Google/Motorola had a functional mockup of basically a Lego kit for phones. Abandoned for lack of general interest.

If you want it DIY, then DIY. The vast majority of people want something that just works. There's a slice of that who care about the specifics, the nitty gritty, the full capability and functionality. I'm somewhere in that surprisingly broad range of a slice. You are too, it seems, but even then my willingness to tolerate jank with the amount of processing power available to literal children these days is extremely limited. My 8-bit NES ran better with only a few spare kilobytes and you mean to tell me actual gigabytes isn't enough room to do flying cartwheels? Sorry, fuck outta here.

Proof of concept is one thing and I can run with that, but daily driver? I need more.