It’s incredibly difficult to form conventional ceramics into “the correct shape to begin with” with even millimeter tolerances because it shrinks twice during production. First when the liquid from the slurry/clay evaporates, and again when the particles sinter together during firing in the kiln. Both of these are non-linear and can cause warping with complex geometries.
EDIT: binders also typically burn off during firing, which further complicates changing shape during firing.
EDIT: binders also typically burn off during firing, which further complicates changing shape during firing.