Small amounts of it are being done, most farms have been no till for years for example, cover crops are the norm now instead of some weird fringe thing, stuff like that. It is not done to a greater extent for two reasons. One is because it is a business and the primary (often sole) concern is making money, so anything that isn't the normal way of doing things is avoided. There are serious financial incentives to not try anything better. In order to actually get a pay out on your crop insurance if your crop fails, you have to have followed all the "approved practices" to the letter. So if it says "spray your potatoes with fungicide every 5 days" and you can't prove that you did, you lose a few hundred thousand dollars this year. This sort of thing makes it hard to change even if you want to.
Second, there's active intent to prevent people from knowing how to do things better. Almost all agricultural inputs are produced by a small number of large corporations. If farmers knew they could cut their fertilizer to 10% of what they buy now, stop buying pesticides, and spend less on fuel those corporations would lose a lot of business. So they pay "agronomists" and "soil scientists" to mislead farmers and keep them on the treadmill. There's lots of very deliberate FUD about organic agriculture, permaculture, etc, and when you've got millions of dollars invested in land and equipment, a little doubt goes a long way.