It's literally because people who have paid for business class want to board first. Think it through. You've just been charged an extra $500 to sit in a chair

It's literally because people who have paid for business class want to board first. Think it through. You've just been charged an extra $500 to sit in a chair for four hours, and you're waiting in line behind a mother with five screaming children? You've got very important business things to attend to! Or whatever! IDK if you ever watched _Veep_ but there's this marvellous episode where a megadonor is complaining that he didn't get more chicken than the $100-plate crowd at a fundraiser. He was literally counting (let's generously say) $5 chicken breasts. Never mind that he was a hominid of roughly the same proportion as everyone else in the room; did not metabolize food any faster or differently; and certainly couldn't care less about $5. So: like that, but for air travel.