It has three advantages over Bluetooth. First, it uses less power so you won't be recharging the keyboard very often. Second, there is no pairing necessary, it's all automatic. Third, it works with just about any device with a USB port, including Android phones. Fourth, the connection doesn't ever drop. The disadvantage of 2.4GHz is that it requires a separate receiver, though sometimes, depending on the device, so does Bluetooth. For example, I use a 2.4GHz wireless keyboard with my smart TV which is a lot easier than trying to enter credentials or search criteria with the TV remote. The TV has no Bluetooth but it doe shave a USB port.
But yes, there is the hassle of charging the batteries on wireless devices. Fortunately, a keyboard is not like a Bluetooth speaker or Bluetooth headphones, it uses very little power so recharging it isn't required very often. Also, you could just leave in plugged into the USB port all the time, constantly charging, so you're no worse off than with a wired keyboard.