Because there is no apparent acute symptom of microplastic contamination inside our bodies that have been identified yet. If microplastics have even a fraction of the harm of actual carcinogens like polycyclic aromatic hydrocarbons (which can lodge in DNA strands), we'd be witnessing mass illness events already.
That's too optimistic to be point of being naive, substances in general only cause damage above certain threshold, so there is high possibility that we are not seeing widespread harm because it hasn't reached that threshold on most people.
Plastic is chemically inert which should raise the threshold quite significantly. The question that needs to be answered is "What does/would acute plastic poisoning even look like?" I am by no means an expert, but I wouldn't be surprised if mechanically it could lead to increased clotting for the same reason sediment clogs pipes.
Even if it requires 'macroplastics' concentrations to cause problems, inert still doesn't mean harmless. One example which comes to mind is that senescent cells are 'inert' compared to cancer cells and they appear to be responsible for /have a role in aging's damage to tissues.
Science has pretty much determined the ill effects of global warming and we haven't stopped that despite the overwhelming evidence, why makes you think there would be a significant movement over this issue -that like you correctly point out its highly speculative-?
We ARE, it's just that nobody cares (or can figure out why)
50% of men will get cancer. Autoimmune diseases become more prolific over time. Fertility has been spiraling for decades. Mental health issues are on the rise.
