I think that forcing the code to run on a 16-bit CPU with few registers and an 8-bit data bus bottleneck is a way to challenge people writing code for this board, while making the challenge worthwhile and fun, rather than frustrating or tedious. That's a tricky balance to get right. I also want to make the programming interface look realistically like something you could imagine as a 1993-era Apple IIGS in an alternate universe where the 68000 and Mac didn't exist.
65C816 is moderately tedious.