Because getting the best grade on a test doesn't get your ass kicked. This motivates you to get good grades in the future. Source: grew up in Russia went to sc

Because getting the best grade on a test doesn't get your ass kicked. This motivates you to get good grades in the future. Source: grew up in Russia went to school there and then also in USA. Doing well on test in USA earns you phyiscal abuse from footballers who were "counting on the curve". Then the school refuses to investigate because football is apparently more important. Doing well in Russia earns you admiration and respect of your classmates.