For various reasons, people want to be able to evaluate students against each other, which requires a total ordering ( https://en.m.wikipedia.org/wiki/Total_order )

For example, I didn't want to go to grad school or work for a megacorp, so I didn't have to worry about my grades. But a lot of my classmates did want those things, which require large scale impersonal evaluation, so they had to sweat about their grades.