It's not because it's useful or something like that
You don't need to know the chart of 1/x² to have a better daily life.
Also, a lot of things school teach us is wrong. For instance, division by zero is possible.
It's a hidden form of competition. Those who care get good grades and good grades will take you to a nice college. If you get bad grades, you obviously won't be able to join Harvard's Club, so you would earn minimum wage at Mac Donald's instead of getting a nice 200 thousand dollars a year with your nice job.
But keep ignorant, do not care about school, so when smart people like me grow up we'll be able to rub our cocks in your face saying "Hey you piece of shit, remember when I studied the whole night while when you were talking about swag? Now you work at Starbucks Cofee and I own a nice car, house, investments and I'm married to a hot wife."