Their keyboards also support BLE with the actual host. Using their dongle has the advantage of working as well as a wired device on a system that isn't yet boot

Their keyboards also support BLE with the actual host. Using their dongle has the advantage of working as well as a wired device on a system that isn't yet booted as you are paired to the dongle not the host, and the dongle then acts as standard USB devices. Putting a more complete Bluetooth host into their dongle would just change the edges of where it is incompatible with normal Bluetooth usage.