That is a bit of a mystery, isn't it? But that's the way of the food industry, like many others (such as the drug industry). Profit is the highest motivation, not the health of humanity.

Although that study establishing the link to pancreatic cancer came out in 2005, experts have known that nitrites are unhealthy for decades, easily since the 1960s. The food industry, and, in America, the FDA, sees more benefit in preserving meats and giving them an attractive red color than in protecting people.