Why we AREN’T doing it went back to the early 1950s. The old Atomic Energy Commission was experimenting with both Thorium and Uranium/Plutonium reactors, and when DOD found they could NOT make a nuclear weapon with Thorium chose the Uranium/Plutonium cycle as a “dual-use” technology. . .
I suppose from the standpoint of weapons grade, if you are going to use it (as we did) that does make sense.
The regulatory regime, for all intents and purposes, precludes the building of a commercial lftr. The regulations are not so stringent for military use, so if they want a mobile power plant that produces 1,300 deg. f liguid for desalinization of water and production of electricity, that might be the ticket to develop the technology.