This is pure speculation, but I wonder if endocrine disrupters present in plastics are leading to a decline in testosterone and therefore decline in fertility (I also wonder how those disrupters affect women)
How is your explanation simple and where is the data to back that? This theory isn’t crackpot, global sperm rates are declining, the average testosterone of men is lower than it was during your grand-fathers time. Certain plastics have been shown to be endocrine disrupters.
Your theory might work in westernized countries but this trend is global according to the article, certain countries enforce more traditional values for men and women and those countries are also seeing a decline.
I'm a novice, but from the research I've done, the evidence is far from conclusive. There is growing evidence of the negative impact of microplastics on human health in a number of ways, but it is a massive leap to claim it is the primary cause for the phenomena you're describing.
In fact, the biggest contribution to declining birth rates is people have fewer children, not men being incapable of having children. And there are plenty of great sociological explanations for that. Changing gender roles, economic mobility, access to birth control, etc.
Edit: As somebody else said, it's a birthrate crisis, not a fertility crisis. "Fertility" is a loaded and inaccurate framing.
PSS: Even crisis is loaded. It just leads to people channeling their existing personal insecurities into large scale social phenomena.
