Really, the greatest reason has to do with organizational momentum. Think of how office politics work when different groups have competing ideas for the same solution. Those with expertise and time invested into their way are going to protect and defend their turf. Thorium lost that battle.
The argument that it wasn't good for weapons integration doesn't hold water as a commercial power reactor would not be used in that fashion at all. The DOE's production of plutonium 239 comes from specialized irradiated u238 rods exposed for 4 weeks or so - totally different production method and process that a PWR power reactor would use.
The argument that it wasn't good for weapons integration doesn't hold water as a commercial power reactor would not be used in that fashion at all. The DOE's production of plutonium 239 comes from specialized irradiated u238 rods exposed for 4 weeks or so - totally different production method and process that a PWR power reactor would use.