IMO the cost and number of uses on throwing weapons are prohibitively restrictive. I have a run nearing 40 days on Brutal, and I've only been able to acquire 2 javelins (12 shots total), due to costs/stock and not visiting vendor at every opportunity.

They can cost as much (or more) than melee weapons with 40 uses.
It seems they exist to keep axemen and spearmen competitive, but with only ~6 shots each, they are too rare to regularly incorporate into tactics. The damage isn't anything to write home about, with ranged falloff and slashing/piercing being the most common resists.

If the number of uses went up (logically they should be more recoverable and less disposable than arrows/bolts) spearmen/axemen could be more worthwhile.