My best guess for why the FTRD hasn't been mass produced is that it's hard to get turning well.
Here is a picture of Eitan's FTRD:
eitan_ftrd.png [ 183.1 KiB | Viewed 912 times ]
This puzzle is 100% equivalent to TomZ's Curvy Copter II.
The issue is that in the Rhombic Dodecahedron version of the puzzle the corners with the 4-fold symmetry tend to be quite loose and easy to rotate in place. Mid-turn they tend to sag and catch. Furthermore, the 4 triangles around those corners have a somewhat awkward mechanism on them and are a bit loose and contribute to catching too.
When the puzzle is a cube like the CC II the trouble pieces are the center squares and they are surrounded by other pieces and not hanging out on the edge of the puzzle like they are in the FTRD form. These aren't insurmountable problems but they do add to the difficulty of making a really good turning puzzle.
Also, the Rua is deeper cut than the CC II / FTRD which hides the 24 helicopter cube triangles and the edge centers. They aren't gone though, they are just on the inside of the puzzle. This would be roughly equivalent to a Pyraminx Crystal in that there is a hidden inner shell.
The Toru is much deeper cut than either and has a lot of hidden pieces. It would be similar to a Starminx in terms of hidden pieces.
I think the complexity of having hidden pieces combined with the somewhat catching / unstable rhombic dodecahedron shape combine to make a puzzle that isn't an ideal candidate for mass production.
Of course it certainly could happen. MF8 is bringing out Eitan's DeFTI and they did release a Starminx so we know it can be done. I'm not holding my breath for an FTRD though.