Earlier quoted context omitted.
Writing defmacro in syntax-case is simple. Writing syntax-case with defmacro is not. Everybody seems to think scheme macros means syntax-rules. You can get something pretty cl-esque with implicit renaming macros, but with hygiene as opt-out instead of opt-in.
Didn't R7RS drop syntax-case?
It just deferred a lower level macro system to r7rs-large.