The weapons lobby has nothing to do with it. The widely talked about claims that Thorium is not usable for weapons is false.

Uranium would most likely be picked for an industrial scale nuclear weapons program for a couple reasons but thorium does not eliminate these problems.

Furthermore many of the benefits people talk about when talking about Thorium is really about the reactor. Many of the same benefits could also be achieved with Uranium.

Thorium really shines for some specific reactor types.

Whats holding reactors back in general is regulation in all parts of the supply chain, from research to operational licenses, and a wide popular anti-nuclear feeling.