If pesticide applications killed many of the organisms, you can't build soil aggregates, and you can't improve oxygen diffusion into the soil. Greens made with sand and little organic matter have few foods to grow the bacteria that make the smallest size soil aggregates, and few foods for fungi that bind the smaller aggregates into visible aggregates. There are no foods for protozoa, beneficial nematodes or microarthropods that engineer soil pores. In just a few years, what little organic matter was present is used up, and the sand compacts like concrete. To open up the spaces between particles, you need to inoculate the beneficials, and provide food.
Soil structure can begin to come back within days as the bacteria and fungi grow.
But be careful - too rapid growth of bacteria and even fungi in some cases can suck up all the N, leading to yellow or dying plants. Balance is critical in the conversion from straight sand to organic matter plus sand.