Microplastics are this generations lead in gasoline. Crappy processed food would be the second culprit, followed by vaping and whatever crap goes into that.
So, can you pay me all that research money now?
Those are great hypotheses. Now prove them likely true with preliminary evidence that is rigorously collected so that it might be duplicated by others, and then you get a shot at research money. With that research money, you then need to perform additional data collection and hypothesis testing in a way that, again, is rigorous, using tools and techniques that are widely available, so that others can duplicate and extend your findings. And if the additional data you collect shows that you were wrong, then go back to square one.
Why? Because we need to be certain that the answers are correct before spending massive resources on addressing them. Otherwise we're just pissing in the wind.
Additional hypotheses that have been tossed around here include the massive increase in sedentary behaviors that are well-documented, the reduced vitamin D that comes with lack of sunlight exposure, the lower immunological development that comes from reduced social contact, etc. There are lots and lots of hypotheses. Let's see some data.
Me? My money is on low-grade vitamin D deficiency, weakening the immune system.