Most likely because there are those who did not select the Precocious Engineer as a companion last year. It's one thing to have a Hallowmas upgrade for a companion/item that everyone who attended a festival likely has; for instance, it's possible to get all the Feast of the Rose companions. However, unless you paid Fate, you won't have all of last year's Hallowmas companions. Especially for festivals like Hallowmas, where you can only obtain some companions without paying Fate, it would be quite helpful to know which ones will be upgraded next year. Otherwise, at this rate, we can look forward to a Whitsun Sartorial Augmentation being the basis of a Hallowmas companion.