>>214
Raspberry Pi
RPi has a massive and questionable binary blob that has to run before anything else. I'd rather look at {Panda,Beagle,Cubie}board instead.
Probably because they're either locked down (cell phone/gaming device) or not popular enough.
You'd be surprised, but a lot of them aren't locked down. It's just that documentation is virtually non-existent and there's hundreds of stupid quirks and workarounds for every single fucking device.