It all boils down to bioaccumulation. Radioactive stuff that just floats around is diluted fast into nothingness.

Chernobyl was bad, but most of the fallout landed on forests and lakes that are not significant source of human food chain (mushrooms, fish in lake and animals in the forest still have traces left).

Fukushima did not blow stuff into the atmosphere, most of the leak is from water leaking to the soil and to the sea. Almost everything living in the sea is important part of the human food chain.