because the product was not manufactured at a single plant (it was made at plants around the world including the U.S.) and the raw ingredients were not from a single source but from a number of non-U.S countries.
Also J&J had been using talc until 2020 when they "officially" switched to cornstarch in the U.S./Canada, and globally in 2022 - Johnson & Johnson Consumer Health to Transition Global Baby Powder Portfolio to Cornstarch
The problem was most likely certain batches that were sold with contaminated ingredients and with such a large market, and without proper and/or sensitive enough testing of the raw ingredients, something like this could have happened.
An example of a different set of faulty testing standards came about during the Chinese milk powder/infant formula scandal almost 20 years ago, when you had shady dealers "cutting" the actual dairy product powder, which is more expensive, with cheap ground melamine (the latter a heat-resistent plastic product often used for dinnerware, etc). The melamine was able to mimic milk powder protein content when using the standard testing at the time. Half a dozen infants died and tens of thousands had renal damage in that incident. IIRC, several of the fraudsters who pawned off the mix, were identified and executed by China.
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