It costs too much to develop, in relation to the numbers to be sold in that execution...
The problem for manufacturers is, that they need to sell brand new vehicles, to people who have the money to buy them..
People who are satisfied with 20 year old technology, are usually the ones with money for a 10 year old truck, so these trucks will never be available as 10 year old used trucks, if there is noone who will buy them brand new...
Case chose to introduce the Magnum with powershift only, and not to make the Vari-Torque prototype of the early 80s (the power split type CVT which Fendt introduced in 1996, coincidently the year that the IH patent expired after 25 years) or to calibrate the tooling of the Rock Island, Illinois IH plant after moving the entire line to the former Case factory in Racine, Wisconsin to make the Synchro-tri-six transmission of the 5488 again, because they ran out of money.... field validation is a costly proces, even if individual components are already on the shelf...