I've long thought that every restaurant/bakery/etc could publish their full internal cookbooks and not see a drop in sales. People don't buy it because they are incapable (or think they are) of making something, they do it because it's faster, they don't have all the ingredients, they don't have the time, they don't have the skill, the list goes on. I bet I could give the instructions, the equipment, and the ingredients to people and they'd still choose to buy it. Sure, you might lose a tiny bit of sales to "home bakers" [0] but I think it'd be eclipsed by people that saw/read/heard about the cookbook (maybe never even saw it) and that was enough "marketing" to get them in the door.
I've always found "secret knowledge" to be a little silly. A sort of, security through obscurity. Knowing a recipe doesn't make you special, being able to build/run a company around it and make it consistently good does.
[0] I love to cook, I sometimes like making copy-cat recipes. I cannot think of a copy-cat recipe that I made more than 2-3 times. While it's fun to do, it's never exactly the same, and I also believe that "food tastes better when someone else makes it". Also it can sometimes be just-as or more expensive to make some food items due to needing a bunch of ingredients that they don't sell in exactly the quantity the recipe calls for.