>>11
I suspect they wanted to standardize the macro-system for portability. In general Scheme standardizers prefer to have one way to express any given idea. As for why hygene was selected, this is probably just because scope is considered very important by the standardizers, and unhygenic macros can violate this. R6RS's syntax-case is equivalent to low-level macros iirc, so flexibility was reduced in R5RS, and R7RS but not R6RS.