A nuclear bomb sends most of the fallout high into the atmosphere were it disperses and is held in circulation for centuries before finding its way back to the ground. This adds to higher background readings.
Fukushima keeps spewing fallout at ground level, into the groundwater and ocean and still is contaminating the surrounding area. The contamination never makes it to the higher atmosphere where the accumulative affect on the ground finds it way to food sources and water supplies.
Why you think going through all the trouble to clean up Fukushima is pointless and should be just left to sit there and be ignored is beyond me.
Study up, Mount Athos. If you do you’ll discover that Nagasaki and Hiroshima combined had a tiny fraction of the amount of radiation already released by Fukushima. If only Fukushima had as little radiation as those two nuclear bombs today - what an improvement that would be!