The modern industrial farming complex is designed to treat every field as identical, and to allow as few people as possible to work as big an area as possible. That allows for standardizing methods and optimizing the output per acre. Tilling the soil is mainly for aeration: the farm equipment rolling over the fields (which is needed to massively reduce labor costs) compact them, so you need to loosen the soil again. It's also for weeding; if you till before you plant you uproot any plants already growing there (weeding by hand is extremely labor intensive). It also allows you to mix compost and other beneficial components into your soil to further aerate it and give space for roots to grow. It's all to give your field a "blank canvas" that you apply your crops to, where you can just dump about 2-3x the recommended amount of fertilizer into it and not worry about the particular conditions of the soil itself beforehand.