You aren't reloading a save and clearing the same area multiple times, are you? Loot is generated randomly, but it's generated on monster creation, not on monster kill. SO if you save a game, clear an area, load the game, and clear it again, you should get the exact same drops. You'd probably need to clear the area, then go do other things, and come back when the Goliaths respawn.
If you aren't doing that, then you just have terrible luck right now with the RNG. Goliaths can drop carapace.