That's because (in my humble opinion), T/D's stuff is "so much better". While Franklin/Covey is much cheaper than T/D, it is also OVER-FORMATTED. They seem to take delight into FORCING people into their paradigm (Priority A, A1, A2, A3, B1, A1A1B2, etc.) and as a result, I have found working with their stuff to be highly frustrating.
I guess I'm a dyed in the wool GTDer (who started with David back in...89) who is still used to the T/D style.
Just my .02!
Kent