Well, I assume because people just haven't been using it that much. I'd never heard of it before you said anything and knowing what it is now ... I wouldn't use it. For one, I wouldn't want anything that the spectator could actually see to be my TR. I'd much rather have it completely concealed.
I can't see anything this brings to the table that I actually need. For less than half the price I could get two regular reels which would serve my needs perfectly. Or, for a small fraction of the price I could get a spool of IET and tie my own loops.
So, if I had to hazard a guess, it would be that it hasn't been talked about more because people just aren't using it that much.