It's an interface. It turns many tasks (get package a to package b) into two tasks: get all the packages to the hub, and get all the packages out of the hub.
It's hard to keep the planes full if you don't do a variation on hub and spoke. It is also expensive to have sorting facilities everywhere.
Could you theoretically be more efficient? Sure. But it's much harder to buy planes, plan new flights, build a new sorting facility and train staff vs you just running your simulation again on the command line with different parameters.
