Hard-core paleoids will ask with a sneer, why do so many low-carbers insist on making substitutes for modern foods? Why doesn't everyone just eat food the way it's found in nature? Why not eat an egg and a handful of nuts and a piece of fruit instead of compounding "paleo pancakes"? Why do you think you need tortillas and cookies and BREAD?
There are easy answers, actually. For one thing, when people first stop eating "conventionally" they don't know WHAT they should be consuming on a meal to meal basis. They eat bacon and eggs with delight on weekends, but on working days...? How do you go from toast-and-coffee or a cereal breakfast to paleo, when you are trying to get a household out of the door in good time? And those damn lunch boxes to fill.... Families with children which, for one reason or another can't have a stay-at-home parent, sometimes have trouble switching kids (especially older ones) to a more healthful regimen -- and sometimes it's another stuck-in-the-mud adult who whines "just because YOU have to be on a diet [you repulsive slug], does that mean that *I* have to suffer?" [sob]
Paleo/LC convenience foods to the rescue! ...Illusions. Nut-flour breads taste good and give the impression one is just eating a healthy version of the SAD. Meal bars and "shakes" have been a part of the American scene for a long time, and seem pretty normal to people who dislike standing out. Alternatives run from the half-assed to some pretty damn good substitutions. They may be a crutch, but if you "can't walk" and haven't the time to crawl, crutches can be extremely valuable.
Arguably, convenience foods are what put us into this mess in the first place. Easy-to-make versions of more time-consuming traditional foods fill our grocery stores: instant oatmeal has largely taken the place of the porridge that used to cook all night over a banked-up fire, and canned soup replaces -- poorly -- the stock-pot that used to hang unceasingly over the hearth, being added-to and extracted-from constantly. A cake used to be a VERY rare special-occasion treat for ordinary people, because not only were the ingredients expensive and sometimes unprocurable, but because the methods involved USED to be labor-intensive and time-consuming. But now there's no more fire to build and wait for till the embers are just right -- electric and gas ovens took care of that problem. The mechanical, rotary hand beater took the place of the whisk and spoon, then the cake-mix came along, then the electric mixer, until the just-add-water-pour-into-included-disposable-pan-throw-it-in-the-microwave turned what used to be something you had to plan ahead for into an everyday impulse confection. Or if that's too much trouble, go to the corner store where you can get a shelf-stable product you just have to tear open.
Though it has become epidemic recently, for millennia people have been making foods in advance for those occasions when it's not possible to hunker down, build a fire and create a meal in a civilized fashion. From historical record, we know that Aztec warriors would go on campaign with their own version of MREs -- chia seeds. Same for pemmican, which is much more nutritious. The drying techniques that allowed northern "Plains Indians" to save their hunted and gathered foodstuffs for winter also provided instant food for days when cooking up a stew would be impractical. Prehistoric convenience food.
The earliest replica cookbook i own, Amelia Simmons' 1796 "American Cookery" already suggests adding ketchup to gravies to round out their flavor, though she doesn't include a recipe for any of the versions she would have been familiar with. Of course in this era they were made most usually out of mushrooms or walnuts, though oyster ketchup was well-known and they'd already begun making the condiment out of tomatoes as well. It was the MSG of its age, adding what we would call "umami" nowadays. I once made mushroom ketchup, which kept indefinitely and was an excellent addition to gravies and soups whose flavors were a little flat. Mary Randolph, in her "Virginia Housewife" of 1824, tells how to make a number of home-made condiments including "fish sauce to keep a year." Cuts down one of the steps needed to prepare the meal. More convenience food!
Napoleon is famous for (among many other things) offering prizes for great new ideas to feed armies on-the-march. This was the beginning of canned foods, though used champagne bottles were the first vessels to be tried, because of the sturdiness of their construction. "Desiccated vegetables" -- or as the troops called them, "desecrated" ones -- and soup stocks boiled down to a powder so that all you had to do was add water, had appeared by the time of the American Civil War. Tins of oysters were a prized commodity on the frontier; the soldier's hardtack and sailor's biscuit much less preferred though their value was appreciated.
Old-time writers of books describing the day-to-day lives of ordinary people -- beloved by reenactors like me, who want to demonstrate the experiences of our ancestors to those of our contemporaries who are fascinated by history -- sprinkle in hints of more grab-and-go meals. Cold fowl, hard-boiled and pickled eggs, cheese, meat pies, johnny-cake (the etymology for which has never been determined beyond doubt -- it might have once been journey-cake), all have their modern equivalents at the drive-thru window. Sherlock Holmes was once observed to cut a hunk of cold meat off the joint on the sideboard, slice some bread, sandwich them together and stick them in his pocket for later. T. E. Lawrence wrote of a fat-and-flour mixture the desert tribesmen carried in a saddlebag. The earliest tamales were a corn-husk-wrapped "lunchbox" food, and all around the world different leaves have been used to protect foods tucked away inside -- sometimes you eat the leaves and sometimes you don't. (Relatedly, trenchers were originally thick slices of bread that luxury dishes were served on; when the quality folks had eaten what they wanted, the juice-soaked "plate" was given to servants and the poor for their dinner.)
Convenience foods have been around for a LONG time, though like so many other things, modern society has taken the concept to extremes, to fit in with our on-the-go activities. I suspect that every culture throughout history has had some sort of equivalent. Eating is essential, and sometimes you have to carry things along for a later meal. It should be something that is compact and hardily portable, won't spoil very soon, will soak up loose juices, which won't require special equipment for consumption and ideally won't make your hands a mess in the process of eating them.
THAT is why recipes for various bread-like products are all over low-carb and paleo websites, why so many nut-flour cookbooks exist. There are few more simply-convenient containers for food than the various styles of bread that can be found all around the world. Tortillas, pita pockets, "coffins" and crusts, or basic absorbent slices are just so equal to the job.