Reverse image for wax carving?

Like Bowie , Hart also appreciates the fact that in metal clay she
can create a positive finished piece, rather than the reversed
images required by wax carving.

Molding Multiples - Using metal clay for production models

why would a reverse image be required by wax carving? to create a
master model by carving wax, dont you carve a postive image, cast
it, clean it up and make mold,inject the wax to duplicate the
positive images, and then cast as many as you wish?

thank you ,Paul