Likewise with other chemicals like tetraethyllead in gasoline. We’ve known lead is toxic since Vitruvius but the first anti-knocking agent was just too useful so everyone kind of ignored it.
That on top of what others said - it's hard to predict effects and their scale before actually doing the thing that causes them. Also, it's only in the last 100 years that we learned that large-scale effects and environmental damage of various chemicals are a thing in the first place; it was hard for people to even conceptualize or imagine such things.
[0] gently bash someone on the head for decades, cut out their brain, notice it's all shrunken and weird in composition ... maybe in a culture with strong warrior and ritual cannibalism practices
Humanity is mostly reactive. Once people are harmed then we launch a decade long fight against massive corporations who gaslight us as to how safe their product is and spend millions in delaying court battles and faking positive public opinion.