Last I read none of the closed plants in the USA had been completely decommissioned. Which is why I think the estimates for decommissioning are wrong. But perhaps there are cheaper ways to do it in the future... I don't know.
Yes, fuel cost isn't that much... apparently 0.52 ¢/kWh. But that could still impact the bottom line if costs were 3x as much. But with 70 years of uranium left, I'm not sure prices will stay at similar prices over the life time of a new reactor.