Efficiency is the name of the game. If every single molecule required its own ATP-powered pump, the cell's energy demands would be unsustainable.
Let’s stick with the Sodium-Potassium Pump example. Because that pump works tirelessly all day, there is a massive surplus of Sodium outside the cell compared to inside. Sodium wants desperately to get back inside the cell (moving down its concentration gradient). That desire to rush back in represents potential energy. primary active transport vs secondary active transport