Left out endless litigation and unpredictable regulatory actions, aka political risk.
That is what killed off thorium research decades ago.
This article is very brief but it does point out that the early research was at Oak Ridge. It was killed in the early 70s by the hawks in Congress and the US military, led by Admiral Rickover who was head of the govt's nuke program, because you can't make nuclear weapons from thorium. The head of Oak Ridge, who was a supporter of Thorium, got fired from his job. Nobody else wanted to get fired so it was completely dropped.
All the data developed was stored away in a warehouse and forgotten.
In more recent times all the data was re-discovered at Oak Ridge because NASA needed a power source other than PV.
Some of it had already been destroyed but what they did find was open source published on the internet.
Wiki page on Thorium-based nuclear power
Thorium: The NASA Story -a 2 hour documentary