Why did 1954's "Castle Bravo" fallout cloud , rather than 1918's Spanish Flu or 1883's Krakatoa, finally convince humans of our interconnected biosphere?

Perhaps natural things don't really matter to us hubris-driven humans.

Because even huge natural catastrophes like Spanish Flu (and earlier global pandemics) and the volcano Krakatoa's volcanic winter didn't seem to count as much in the human mind as did a relatively small disaster that humans themselves were causing.

The unexpectedly large yield from the American thermonuclear test Castle Bravo in 1954 led to a strong plume of radioactive dust to fall on a Japanese fishing boat thousands of miles away, quickly killing one crewman.

It also added a relatively small amount of a much longer term radiation killer, strontium 90, to go high up into the atmosphere and then slowly fall all over the world, onto grass and then into cow's milk and eventually into the growing bones of babies.