Slings, pebbles and stones

Hello! Just got back to cataclysm after about a year or more. One change I’ve noted is the sling now shoots rocks instead of pebbles. Any idea why the change?

Based on historical sling ammuniition it doesn’t seem realistic to me:

Probably because the definition of a pebble in the game is a 10 g item, while the rock is a 657 g one, so out of one item that’s way too small (used by slingshots) and one that’s a bit too large the latter was used.
I wouldn’t be surprised if there would also be a deliberate decision to make it inconvenient to carry a large amount of ammunition for it.