If you properly fair a fixed undercarriage it has a pretty low drag. compared with the additional weight from the structure, machinery and systems for a modern retract it saves significantly in terms of weight and cost.
Given it has a parachute it also offers a significant near guaranteed energy absorbsion on its final descent - getting that sort of energy absorbsion any otehr way would probably be impossible.
Look at a number of the older Cesspits and see just how little performance is gained from un-faired undercarriages compared to the equivalent retract - at under 200 knots its a wate of time lifting the legs.