Anyway, WiFi actually operates in unlicensed spectrum, not in WiFi-specific spectrum, so continuous carrier waves would be legal too.
The same way it would know where it is with the 6240-6740 MHz beacons.
The beacons probably output a continuous wave of a certain amplitude at that frequency. This would be classed as interference on at least the wifi spectrums so it is not allowed.
That's why you send actual 802.11 messages instead of a continuous wave.
And how do you determine your location based on an 802.11 message?
The same way you determine a location based on any regularly occurring radio signal (in fact, the same way they propose to determine location in their requested spectrum). The only reason to encode a proper 802.11 message would be so as not to interfere with other devices in range.