[TeMPOraL]

We're still to identify any meaningful effects of microplastics other than them being everywhere and looking foreboding.

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.