Building warbows and arrows is expensive. Training archers for the military tales a long time often they started at 7 years old! Warbows were around 150lbs of pull, not many average guys could pull one back, let alone shoot it accurately. Hence, skirmishers using slings, javelins and darts were MORE EFFICIENT! They took less time to train and the equipment was cheaper to manufacture.
Look up “Swedish dart” esp. on Youtube for directions on making and using, Dave Canterbury even has vids on them. The string is wound around the dart, hence giving it spin as its launched. The dart gains stability quicker allowing it to be more accurate and travel further. The mass of the dart aids in extra energy for deeper penetration.