Why is this not implemented?

[Super]

At first I would assume that the 'A' & 'B' sloped curves were sold only in sets that had a particular Layout that only incorporated those directions of curves (like the double spiral in the Amtrak set) but if I remember correctly, didn't they also sell these curves by themselves as a track accessory?

I would like to see the 'C' & 'D' made but what I most wanted was the 'B' sloped curve made in the light grey. I don't think they ever made one, at least I haven't seen any. They do make the 'A' sloped curve in light gray of which I have many so it was impossible to make a double spiral (like the one in the Amtrak set) in all grey track.