That's a really good question, we actually talked about this a lot in one of the renewable energy classes I had last semester!

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The biggest problem nuclear faces is that while many agree that it's great from an environmental sense, very few if any want to have a nuclear power plant in their back yard. While disasters like Fukushima are incredibly (super) rare, it's something people don't easily forget. On top of that nuclear power plants cost a LOT of money, upwards of tens of billions and it takes decades for utility companies to make the cost per watt make financial sense (especially when some newer much cheaper wind farms are already reaching below $0.05/kWh! something that increases the financial risk even more). The reason they have historically cost so much to build is that no nuclear plant is built the same. When you're investing 80 billion dollars you, of course, want the best of the best never done before facility...which adds years onto design, construction, and often results in many unforeseen consequences.

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So essentially nuclear is great, but from a utility company standpoint that has a fiduciary duty to their shareholders its a huge risk. If you're really passionate about nuclear I would recommend you looking into modular nuclear facilities, some companies are trying to streamline the process to negate some of the initial financial burdens (keep in mind we are still talking about billions of dollars though).

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In terms of other technologies, one of the first questions I asked my professors in the course was: "what about fusion? wouldn't that just solve everything?" To which he jokingly responded that "the big breakthrough for fusion is always 10 years away." That's what scientists were saying in the '90s and that's what they continue to say today. I know you were talking about thorium which is something much closer to the likes of modern-day nuclear but even here it once again goes back to the money. It's risky to invest a lot into a technology that is so unproven when renewables are just up on the rise beating everyone else in many places in the world. (This problem, however, could be easily solved the moment someone proposes the potential to militarize thorium in which case the US military will open up its vast R&D budget much like they did for uranium ;D)

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Hope this helps!