Read a very interesting,if dry, book about thorium recently.
Basically we ended up with uranium reactors because the military wanted to make bombs and thorium reactors aren’t good for bomb-making.
I think it is probably the military uses at the beginning maybe in to the late fifties because their was the fear that the USSR was producing more bombs that us. But later I think it was that so much had been invested in Uranium LWRs that it was considered to late to turn to Thorium.
On the commercial side all of the engineers had been working with Uranium recators for a decade or more. In the colleges Uranium had been taught to up and coming reactor engineers. Thorium was barely touched (I have some text books from the 1960s. They are more like pamphlets because I don’t think they had written the text books yet).