I'm of the impression paper bags are not meant to be carried. As long as I've been alive, they always break.

I suspect they're simply supposed to be a bundling device so you can stack them for loading in one of those foldable vertical bring-your-own-grocery-cart like old ladies in urban areas use. They certainly can't carry all that crap in-hand either, but this is the only way I've seen paper-bagged groceries make it more than a block without drama.