If Dr. Brand knew Cooper, and knew him well enough to know that he was capable of flying the mission, why didn't he just contact him? It seems like they were pouring a ton of resources into the program, why weren't they also reaching out to and training pilots they already knew? Especially one who lived relatively close to their project base.
The script and novelisation would strongly suggest that NASA were simply unaware that Cooper was still alive, hence their failure to contact him.
With the collapse of the previous NASA structure and the "off the grid" nature of his farming lifestyle it seems likely that they just lost track of him and assumed he was dead.
"We need a pilot. And this is the mission you were trained for.” Cooper thought back to his training. Sure as hell no one had ever mentioned anything like this to him. He’d thought Mars, maybe, or Europa at the outside. “Without ever knowing,” he said. “An hour ago, you didn’t even know I was still alive. And you were going anyway.”