For one, you have to provide one specifically for your board to boot at all. There is no "common" one that'll get you to a shell on any board. The main issue i

For one, you have to provide one specifically for your board to boot at all. There is no "common" one that'll get you to a shell on any board. The main issue is that most SoC vendors just dump a heavily hacked up Linux kernel source intended for Android on you, along with binary blobs (firmware, android hal services, etc.). The drivers aren't in the kernel per se, just enough of a stub for the proprietary blobs to talk to the hardware. So if the goal is to run a standard Linux distro on the board, you're pretty screwed unless you have the time and resources (or a community) to reverse engineer the android bsp into drivers for the mainline kernel. The thing that makes the RPi great is that there's actually an entity paying for this development to happen, along with the community. It's certainly far from the fastest ARM board, but even the decade old RPi 1 still gets kernel updates.