I think you're right to believe that because it is true and I skirted over why I believe it takes generations.
It is not impossible but difficult to document how to do effective farming because every farm has its own individual needs. And what may be true for one farm will likely not be true for another. Hence relying on first hand knowledge, albeit extremely fallible, is more reliable than reading a book and then destroying your crop for a year. (Obviously farmers read, study and improve)
The main reason would be location.
- How does water irrigate around your property? Where is the clay? Where does the water lock in when it sinks in different acres? What happens when there is a drought in this area? What happens when it floods? What should you do when there is extreme weather?
- What makes the soil in this locale good? What is it naturally good at growing? How should you replenish the soil? What native wildlife contributes to the soil? What insects plague the area and do they have decade long life cycle bursts? What to do when a swarm of locust come?
- When does your first frost generally occur? What plants can you grow through a frost? Maybe Kale will survive because although there is frost, you live in a valley where the humidity is higher so the Kale can live. You can't grow X crop because the wind is ever so slightly stronger every 5 years because of atmospheric shifts.
And just to make it more fun, sprinkle on the problem of economics(supply/demand) and logistics.
Also it would be hard not to meet a farmer who calls it a "way of life" because it absolutely is. They live far away from the spoils of civilisation, work incredible hours and live isolated lifestyles. They laugh at city folk because a city man "wouldn't last a week on the farm", which is probably true. Fun fact: Australian farmers have twice the national suicide rate than the average man.