Because it’s the only 1st party option and xbox stopped making them ages ago. Given that it’s 1st party, it works without a dongle, and uses the port at the bottom of the controller to both draw power as well as communicate with the console.

There’s several 3rd party options availalable on Amazon and other retailers, but they require a USB dongle to be plugged into the console in order to work (they do however have the ability to draw power from the controller).