You grow each year a different crops, because they have different fertilizer requirements (and some even fix Nitrogen) and also helps to reduce some plagues. It's also possible to plant different crops in succession, so you get multiple harvests in the same year.
> One take-away is that agriculture as it has been practiced is about the dumbest way to grow food. [...]
One very useful technique in modern agriculture is crop rotation. https://en.wikipedia.org/wiki/Crop_rotation
You grow each year a different crops, because they have different fertilizer requirements (and some even fix Nitrogen) and also helps to reduce some plagues. It's also possible to plant different crops in succession, so you get multiple harvests in the same year.
For these, a perennial version is bad.