Because most people aren’t as productive as Worker B.

Having Worker B come in late and leave early sets a bad example for all the Worker As (and breeds resentment among them). Worker B staying all day and screwing around half the time and distracting Worker A so they get 8 widgets done an hour instead of 10 is bad, too.

Give me 10 average people over 5 great ones any day. Average people can get better when they work together. Great people get bored and move on. Average people are just fine for most jobs.

And I assure you that I’m decidedly average and unspectacular in every way.