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).
Tis needs to be a private investment. Govt will not fund these studies since they would undermine the billions in subsidies to windmills, solar companies, etc that throw donations to the Dems