because buggy body is less likely to be damaged after accidence.............. when touring crashs, the shell breaks, when buggy crash, the skeleton breaks, the shell is intact.
more important, more people play on-road than buggy.
and one touring body almost fits all touring car, but one buggy shell just fits one particular buggy model
so.......that means models shops are not willing to stock all different models of buggy shells .......in order to avoid "dead stocks" in future.............