That is not to say you won’t be able to find the set in stores, or that the product will be scarce (distributors still have plenty of it in stock). It’s just to say that Pokemon printed enough of it to meet longterm demand and won’t be making more of it.
Usually TPCi creates several print runs of sets, which is why this is news. For example, they were still printing 2017’s Burning Shadows up until recently. But with Team Up and Unbroken Bonds, they cut off production earlier than ever.
Speculation for TPCi’s decision is that they are transitioning to a new production style, along the lines of how Yu-Gi-Oh produces their sets. Instead of making an “educated guess” about how much product to make, it seems TPCi will be taking all preorders from distributors in the future and printing only that demand (plus some extra on top of it). Then once a set is printed, that’s it.
The reason for this could be to eliminate overproduction. If you’ve noticed, most promo products still use booster packs from the XY era. There are also several sets that Pokemon overproduced that do not sell well with distributors, such as Fates Collide and Steam Siege. By capping how much they print, TPCi eliminates both problems.
Unfortunately for sellers, working with TPCi is problematic because the company doesn’t stick to one production style like Wizards of the Coast or Konami. Sellers don’t know what TPCi will or won’t do, which can cause massive losses for shops. Usually TPCi keep printing sets… but sometimes a set goes out of print the day of its release (Ultra Prism). Sometimes a set goes out of print then TPCi revives it years later (Roaring Skies). Sometimes they decide to stop printing a set shortly after its release (Unbroken Bonds). But hopefully TPCi will be sticking to the current trend from now on.