Why do cell after an extend stop conducting electricity?

Cells drive the current through a circuit. If they run out of power, who is gonna give the current. They work on a chemical reaction that takes place inside them. As you may recall, in a chemical reaction, reactant gets converted to product. A cell is filled with reactants when you buy it. When you use it, the reaction starts and drives current through electrochemical reactions. After a while, its reactants get depleted and the cell dies and you, cold-heartedly, replace it.