Power zoom is common on fixed-lens compacts mainly because of size and design. Small cameras are usually held by the body, so a lever is easier to use than trying to turn a tiny ring on a small, often retractable lens. A motorized design also fits well with collapsible lenses that tuck into the body.

On interchangeable-lens cameras, the usual handling is different: right hand on the body, left hand supporting the lens. In that setup, a manual zoom ring is easy to use and generally works better. Manual zooms are typically faster, more precise, and quieter, which matters because ILC lenses are often larger and heavier and performance is prioritized.

Power zooms on interchangeable lenses have existed, but they’ve generally been less popular because they can feel slower and less precise for still photography. Their smoother, controlled zoom speed can be useful for video, though, and some systems have offered them for that reason.

So the short answer is: fixed-lens cameras favor compactness and convenience, while interchangeable-lens cameras usually favor speed, precision, and direct manual control.