Though even that is complicated by 50 or so years of nuclear weapons testing, which likely also increased cancer rates. Not to mention all that lead everywhere. Produce gradually losing nutrients because farming mostly just focuses on the big three with fertilizer and the others are being mined out of the ground and sent to landfills, septic tanks, waste processing facilities, cemetaries, and crematoriums also doesn't help (though I'm not sure waste processing and crematoriums remove those nutrients from the cycle like the others, since the one could produce fertilizer and the other might be sending it out into the atmosphere where it could eventually end up back in the soil).

There's so much chaos that it's hard to isolate causes, which then makes all the causes kinda "hide in plain sight" because they can perpetually blame the others and shit only gets worse over time.