> A 1950s project is to blame

Half-way through the article: "When the sugi and hinoki forests were first planted in the 1950s and 60s, they weren't meant to stand forever. At the time, it was assumed they would be gradually cut down and replanted over time, as had been the case before the war. But as Japan's economy boomed in the late 60s and 70s, major cities like Kobe and Tokyo grew rapidly, and it ended up being cheaper to import wood from other countries such as Malaysia and Indonesia."

As often in environmental health, the cost-benefit ratio is calculated after the exposure is widespread, i.e. too late.