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

Answer: A higher stall speed forces a faster approach to keep the same safety margin

Extra drag slows the aircraft so much that it needs more thrust and speed — 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.

A higher stall speed forces a faster approach to keep the same safety margin ✓ — Right. In steady flight, lift has to balance weight, so a heavier airplane stalls at a higher speed. With flaps already set for landing, speed becomes the practical lever for keeping the same margin above that boundary. This is why reference speeds are not universal numbers painted on the runway; they depend on aircraft state.

The wing on the same model effectively shrinks as the load grows — 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.