They use higher-caffeine beans for decaf coffee - Robusta instead of Arabica. Robusta beans aren't considered as good so they're cheaper, and they sell the caffeine they extract to e.g. soda companies.
Just not true. Cheap coffee is already robusta anyways, and arabica is used in good quality decaf coffee. Even still, arabica is consistently used as a marketing bullet for coffee… even if there’s plenty of really really bad arabica coffee out there.