This board performs well on 32-bit, but why not build 64-bit?
Because Amlogic doesn’t provide or develop any 64-bit drivers for any of their chipsets.
Android (on all recent Amlogic kernels) runs 64-bit kernel and 32-bit userspace. There’s nothing to stop people building 64-bit userspace, but then you lose compatibility with a ton of essential libs and apps which are only available in 32-bit format or are badly written around the assumption that userspace is 32-bit, and most people want a functional product. 64-bit would be better, but unless Google issues an edict saying devices must be fully 64-bit the ecosystem will continue doing 64/32.
What essential libs aren’t 64-bit?