By human emotional calculus, it is better for a million people to experience on average 0.001 of a mortality event than for 1000 people to be killed outright.

When we measure such things in terms of "increased cancer risk" and "possible thyroid dysfunction", it is far easier to discount, particularly as young people are not tremendously concerned when people above a certain age die of diseases that are already typical in the aged.

So even if we knew it exactly, people would still care less. It might be more relevant if, instead of death toll, it could be given a money value derived from additional healthcare expenses for exposed individuals, because young people implicitly know that they are the ones who pay when old people get sick.

Same thing for the death toll from coal burning plants. All that ash, deaths from that radioactivity and lung disease, deaths caused by global warming, etc.

If you look at a long enough time scale, anything can seem like a giant problem.