Fairly simple question, why do the Neitos not have javalins?

I understand that the Celts, upon realizing that their borders were coming under attack, decided to put focus into creating professional armies with better armor and better equipment than light Gallic soldiers, but the thing is, why would they not use javalins before engaging the enemy with their swords?

The tactic of throwing javalins before engaging in melee combat seems to have been historically quite effective, which is why the Romans and so many others used it, so why would a professional army unit like the Neitos not utilize such a basic and effective tactic as throwing a few javalins to weaken the enemy line before engaging them with their swords?