Sports drinks don't have nearly enough electrolytes to combat dehydration and are filled with far too much sugar. The average 12oz bottle of Gatorade, for example, has 21g of sugar and only 370mg of electrolytes.
In a recent study, researchers concluded that the extraordinary amount of sugar in most sports drinks was unnecessarily high and that was likely so purely for consumer preference. Based on their analysis, almost no one should drink sports drinks for hydration (except for the case of extreme endurance athletes).