Next - presuming that you bought something from Amazon, why do you need the barcode? If I recently bought and/or regularly buy granny smith apples from Fresh, it's quite easy to figure out the most probable buying targets for queries of "apples." Further, if I regularly buy 5 different types of granola bars, now I can use one query and a checkbox instead of scanning each box individually. (Sidebar: how do you use Dash to scan produce that you've already consumed? Do you have to keep the containers around?)
In the big scheme of things, figuring out which product you probably want to buy based on your buying history (and that of others) is a trivial problem compared to the other problems that had to be solved for "always listening" and such. Amazon's job ends up being the easiest in that stack.