AFAIK, no market to justify production of 120.
There used to be processing plants around the world running 24/7/365 to turn out Kodachrome slides. This has vanished. And, don't put the cart before the horse and say the processing decreased because supply was cut. Kodak could not sell a new Kodachrome 400 film with a big improvement in quality in the late 80s due to decreasing customer support.
Why make something you are losing money on?