China and India are going nuclear, using Thorium, US did this in 1964

Thorium based molten salt nuclear reactors (MSR) have multiple built in safeties against meltdown or explosion and actually can in theory provide more power per ounce of fuel than uranium based reactors. Why isn't the US doing this anymore? B/c the government regulations for nuclear power plants are all based on the Gen II Westinghouse uranium reactor design and its mods, generating electricity from a new style of reactor would almost be impossible in the US b/c of bureaucracy (the H3TR project in Texas is a proposed research reactor using thorium coated beads, but is not an MSR).

Of course, its not a mature technology, but how is it going to become one if no one in the US is funding it?

No emergency cooling system is needed, which is both expensive and adds thermal inefficiency. In the basic design, an MSR generates heat at higher temperatures, continuously, and without refuelling shutdowns, so it can provide hot air to a more efficient (Brayton Cycle) turbine. An MSR run this way is about 30% better in thermal efficiency than common thermal plants, whether combustive or traditional solid-fuelled nuclear.