Anyone who is familiar with kashrut knows that only vegetarian foods (with a few exceptions) are reliably kosher, because it takes very little to make them kosher, just paying for an inspection and certification to say that there aren't any animal products. But if you want kosher meat, kosher cheese, kosher wine, or kosher cooked food, it's significantly more difficult to find that.
Why?
Because those impose real costs on the producers that force them to change their practices. If you want kosher meat, that excludes pork and animals have to be treated differently. If you want kosher cheese, it can't have rennet (an animal protein), which most cheese does. If you want kosher wine, it needs to be processed in a specific way. And if you want kosher cooked food, not only does the restaurant have to follow all of those rules but they also can't serve milk and meat together. Suddenly, it becomes a lot less common to find kosher food if you actually care about it and aren't just cherrypicking an example for a book.
If you want a real lesson from kosher food, it's that companies will adopt all sorts of certifications and make any number of promises as long as they don't have to significantly change what they're doing. But if you ask them to do something that would really cost them money, then they are much less likely.