Two reasons:
1) Star Sapphire's an ingredient which is...More or less extremely hard to come by.
2) It's a tier0 HQ which means it's going to take a lot of luck to HQ one within a small amount of synths being required.
The Star Sapphire bit alone's pretty much killing this synth by not allowing the bonecrafters that want to make these as often as they want to.
