It's a matter of best use. For instance, if my farm is 100% Class I soil and I have good water, devoting 10% to "nature" means 10% less production and additional cost for preserving that land applied against productive land. Then, that production needs to be made up somewhere else. What is of greater environmental benefit, a 10% patchwork that really isn't "natural", reduces efficiency, and increases cost of food, or preserving contiguous swaths of land in its natural state?

Now, if a significant portion of my land was marginal for farming and there was an incentive for maintaining it as natural habitat, that's a different matter.