The Desolate Sea is infamous for its hostility, not because of monsters but the area itself. Thought to be random and indiscriminate, the Sea will fight back and beat down any who passes through that don’t meet it's requirements.
Legend has it that an elder dragon of old rested there after a fight with an ancient being. Unfortunately, the dragon was unable to recover and passed away in the sands of the Desolate Sea. With the blood and body of an elder dragon combining with the earth, the hate and anger the dragon animated the area and changed the Desolate Sea forever.
When the Sea disproves of someone, it will not just swallow them up - but rather wear them down. Temperatures rise, windstorms kick up turning the sand into deadly winds of glass shards. These plagues will follow them through the Sea until they are either no more, or leave.
There have been some that claim upon enduring the trial for long enough, the Desolate Sea will "accept" you and abate it's fury. Though no one knows if this is fact, it does make sense considering elder dragons were lofty beings who looked down on all other races as lesser beings, rarely respecting them.
Strangely, though many have perished in the Sea, there are never any traces of their existence. Maybe the desert also obtained the greed and hoarding of dragons too, but that would also mean…somewhere in the Sea there might be a large treasure to be found.