Im not positive, but methinks creationists equate macromutation to speciation. So while theyll countenance minor biological changes (micromutation) over time, big transformations are rejected: separate species were authored by god and cant occur naturally.
Which is a tad odd because it
seems creationists rely on speciation to make the Noahs Ark myth work. By their reckoning, Noah just needed to preserve representative kinds - a vital space-saver aboard a vessel with limited space. Thus for example, only a breeding pair of non-descript cats had to be saved; and eventually, these diversified into lions, tigers, cheetahs, felis catus, etc. But this would be speciation/macromutation. And very fast macromutation at that. Allegedly, the Flood occurred around 4300BCE. Yet by 3000BCE, Egyptians were depicting domestic cats in their art.