The article suggests several possibilities, including increasing use of antibiotics, and less consumption of salted/cured meats, but the actual answer is unknow

The article suggests several possibilities, including increasing use of antibiotics, and less consumption of salted/cured meats, but the actual answer is unknown. And actually that is the crux of the article: it's not that doctors aren't thinking of possibilities to explain the reduction in disease, they just don't know for sure which of the possibilities they are. Basically, if we've thought of a possibility in the last 20 minutes since reading the article (or headline), a doctor has probably already thought of it, too.