It's a drop chance... this is why FFXIV will never be able to reach a point where casual-meets-"hardcore".
Players QQ that there is no "farm-able" content. SE gives it to us. Players QQ* because it takes too long.

*Yes, this is a QQ post.

Though I rarely agree with Jinko, he's absolutely right. You ran the dungeon way too many times with little break that you just got pissed off at SE for no reason. Geez, put the game down and take a breather!