Why don't monsters pick up their own ammo?

[Pollen_Golem]

This is especially noticeable with Urug. It's easy to stairdance, letting him throw his javelins away. After he runs out of javelins, you can heal and go back to fight him. He is much less dangerous without javelins, but he doesn't bother picking them up after throwing them. It should be easy to program monsters to pick their own ammo back up, but what do I know? I'm not a dev.