Probably because the solid measures are related: 16 oz = 2**4 = 1lb and 1/16 oz = 2**-4 oz = 1 dram.
Yes, I know that, “a pint’s a pound the world around” and all that, but it doesn’t really have anything to do with whether to keep measuring gold weights in troy ounces. I guess I’m not as fascinated with powers of two.
Anyway, they’re your proposed amendments. Personally, I’d like to see all of them enacted, even with the specification of avoirdupois weight for gold, but I’d like to win the Powerball lottery, too, and there’s just about as much likelihood of that.