OR: What if Pepsi decided it wouldn't make economic sense? If they produced a product that tasted like the Coke, then Coco-Cola would've had to slash their products' prices to compete. Then Pepsi would've been left with the choice of either reducing the prices of their products to match Coco-Cola, or not compete. The result would be that both companies' profit margins would've crashed.
For Nivida however, knowing AMD's stuff allows them to implement what made AMD's GPUs and CPUs strong, and avoid drawbacks that weakened AMD's products. The trick is to not get caught by AMD and have the court stop all sales of Nividia's products that used AMD's information.