In a country like France, you can't normally sue to stop a nuclear plant being built. Once the government decides to build it, they have sovereign immunity from suits in their own courts. So if you don't want it, you can agitate for the government to stop it, but you can't sue the project to stop it (or at least, there are many fewer ways to do so). The U.S. by contrast has waived its own sovereign immunity in a lot of cases, setting up a more decentralized decision-making process where the legislature passes general laws, agencies like the DOE and EPA are delegated rule-making authority, and courts then adjudicate disputes. The multiple levels of government (federal agencies, state agencies, federal courts, state courts) add another complication.
If utilities were made liable for harm for nuclear disasters, how long do you suppose it would be before every last one was decommissioned? I suspect all the cost savings TFA hopefully imagines vanish in comparison to the cost of liability.
I also note TFA makes no attempt to express the South Korean costs in USD terms. It wouldn't surprise me, given the state of South Korea's economic development in 1971, if what the graph depicts is not a miraculous decline in costs, but a predictable trend toward the global norm.