It's because it is 4-6m per synth and almost impossible to sell the NQ even at a significant loss. This is compounded by the fact that ingots only drop from VW people rarely do and Legion. So I wouldn't hold my breath waiting on a bunch of these to appear.
Additionally it requires gold to 104 to tier 1, which is 2 levels of silver cassandras at 200-300k loss per synth.
Kaerin: At a 103 level craft the crafter needs 114 skill to reach a 7% chance to HQ these. With the cost of mats these days and the fact that most of the hexed items use the same mats, it'll be a little while before you see these running around. There is the shaper's shawl to help people level up... but it's still going to be a while.
The goldsmithing hexed pieces that require black armor (high smithing) and Ormolu Ingots only drop in Legion (Hall of Mul)are hard to get because no one really sells or farms the materials to make those. It's also huge losses to skill up goldsmithing past 100. If kunwu ores were abyssea drops and Ormolu Ingots were more common, then we would see more hexed pieces. Also this requires Goldsmithing 104 and Leathercraft 40. You would need 114+ to tier 1 HQ.