I'm not a dev, but I'd be willing to bet this is more of a balance concern than anything else. Arrows and bullets are ammunition for weapons that do not benefit from strength modifiers for damage, unless they have the Mighty modifier. Thrown weapons have no limit to the amount of strength damage bonus they can gain. Additionally, thrown weapons can be used with shields for maintaining high AC.
It seems too powerful to me, compared to other craftable ranged weaponry.