Then there is the Theory of Bounded Rationality which tells us expertise may exist but resources, time, energy, info, attention etc etc may not therefore bounds and limits of expertise alone must be recognized and solutions reached are satisficable rather than optimal. Aiming for optima when other factors havent been sorted just creates new problems.
Grandma doesn't bake with "common sense", she is using the specialized knowledge of cooking & baking.
You've clearly never baked before. Baking is a chemical science. You have to adjust temperatures for your freaking elevation relative to sea level. Granted some recipes are pretty forgiving, sure, but far from all, and some are downright merciless in terms of complexity and effort required.
Even people who do it constantly have items that just don't turn out because it's legitimately hard shit.
If making sourdough were 'common sense' then _everyone could do it correctly on their first try_. They don't. Most fail and never try again because the skill level required for sourdough is too high.
I'm an _expert_ cook, but I'm still having to go through the frequent failures of learning how to pickle with brine (fortunately, my failures have been mostly edible and have not turned moldy). Even vinegar pickling requires a certain level of expertise before you can do it successfully, even though that level of expertise is _roughly_ "knowing how to boil water".