Misinformation abounds on this
Daedalus is correct, there's a little more to it.
The US has plenty of ore itself - there have been several miners working it, last I heard of was MolyCorp.
The thing is, worldwide, it seems all or nearly all RE ores also have significant thorium in them - so not only is it hard to get the RE's apart from one another, you have this waste product that most people are pretty fearful of, it's fairly radioactive.
US regulations have shut down our miners and processors by making the cost noncompetitive.
China was cheap...so no one cared much. They are not stupid. For one, they've begun (awhile back) trying to sell only value-added products - magnets instead of the elements for example, by pricing the raw stuff higher, and for two - realizing the current situation, no competition because they drove them all out of business, can be a potent bargaining chip with the rest of us. Whether deliberate or not, it is what it is. Same idea as WalMart causing all the Mom and Pop shops to go out of business, looking around, and then raising prices (or Amazon, or...the idea is the same regardless of the actor).
Those who want to use up the thorium in breeder reactors need to lend me some of that they are smoking, or maybe it's just lack of education. Breeders all melt - 100% have. U 232 which is that Th breeds into is weaponize-able, and fission products are a little different from that, but just as bad. We're not short of uranium and aren't building more plants...hmmm. I could easily debunk molten salt but it'd take a long post to describe how that chemistry utterly fails when atoms are split - which one gets the fluorine/chlorine/whatever? Does it eat the reactor walls in the meanwhile? How do you add more as the number of atoms increases with fission? What about radioactive noble or electronegative elements in the products. Their dream is pure fantasy. If we want the stuff, we're just going to have to stash the thorium till we find an actual profitable use for it.
I do nuclear work for a living. India's been trying to get the thorium cycle working for a couple decades. I say let them figure it out first on their dime and with their lives.