Why does the same model of airliner usually need a faster landing approach when it is heavier?

Answer: More lift must match weight

More lift must match weight ✓ — Right. In steady flight, lift has to balance weight, so a heavier airplane needs either more speed, more lift coefficient, or a different configuration. Once flaps are already set for landing, speed becomes the practical lever for preserving margin. This is why reference speeds are not universal numbers painted on the runway; they depend on aircraft state.

Its wing is effectively smaller — No. The wing on the same aircraft model has not shrunk; the load it must carry has grown. That distinction matters because the cure is not a hidden geometry change, but a higher speed or lift setting to make the same wing support more weight. Same-looking aircraft can therefore use different approach speeds.

More drag slows it too much — Not quite. Drag affects thrust settings and descent path, but it is not the main reason a heavier same-model jet uses a faster approach. The reference-speed logic starts with stall margin: a heavier airplane has moved that boundary upward. Speed is the practical lever once the landing configuration is set.