Why Do 12" Tonearms Cost So Much More Than 9"?

Cleeds, before you suggest that I am silly I suggest you carefully review Schroder's patent so you know what you are talking about.

Cleeds, I am not sure what you are thinking, but just to be as anal as possible, I need to say that pivoting per se is not the cause of the skating force.  The skating force is first of all due to the friction between stylus and groove; I am sure we agree on that.  The friction is in a direction away from the stylus tip; the friction force wants to pull the stylus and cantilever away from the cartridge body and tonearm.  To resist that force, a counter-force is exerted by the cartridge/tonearm in an equal magnitude and opposite direction. The skating force is a vector generated as a result of that force resisting friction, because of the fixed headshell offset angle and also because of lack of tangency of the stylus to the groove. When a straight line can be drawn through the longitudinal axis of the headshell to the pivot point, and when the cartridge in that headshell is tangent to the groove walls, there is no skating force.  Among "conventional" pivoted tonearms, only underhung types, which all have zero headshell offset, ever meet that criterion in actual practice.  For such tonearms, that condition applies for the brief moment when the stylus is tangent to the groove.  For pivoted tonearms that work like the Schroeder LT or apparently the Reed 5T, that condition is constantly met across the surface of the LP, if they are perfectly set up. So, ideally (given diligence in set-up), those latter two tonearms would not generate a skating force.

Thanks for all the information on the Schroeder LT arm Mijo.
It looks and sounds like a near endgame proposition.
But.....$15 large?
Unless the right numbers come up on the lottery I doubt I will ever be giving one a test drive unfortunately.

I think they are somewhat less. I have a relationship abroad who say I can get one for $10,000 (wink wink). I'll have to pay VAT tax up front but I'll get it back in several months.
The dealer in the States is Xact Audio  https://www.xactaudio.com/analog/
He sells it with or without his own turntable but he modifies the arm replacing the wood for a magnesium arm tube which I am really not crazy about.  He has some kind of relationship with Schroder apparently he can sell them here in Magnesium and Frank can sell them in Europe with wood. As for his turntable there is too much mystery about it for me to be sure. I think if I could afford to today I would get a Dohmann Helix 2 and put an LT on it. That would certainly be a last stop turntable.
Not to worry Uberwaltz. This type of design will work it's way down market. Reed is working on a less expensive version now called the 5A.
It is another passive design energized by groove friction but it uses a dizzying series of arms and bearings to do the job. The Schroder is certainly a more elegant design. You have to love the magnetic track trick. One magnet + one bearing vs a bunch of arms and bearings.
The 5T is however a beautiful arm and boy does it work. It is $20K and very complicated but still a grand exercise of applied technology. 

And Uberwaltz, Franks other arm are also genius. Check out the CB. You can get one for $5000 and it could easily run for best pivotal tonearm made.