WSPR on HF makes sense down here on the surface of the planet because certain ranges of frequencies (not the same range always, but generally always within HF) can bounce off of upper atmosphere layers and pinball back and forth to get signals to someone or from someone who couldn't be seen line-of-sight because of the curvature of the Earth. For line of sight work, the 2.4GHz in theory would work as well as anything, but another trick WSPR has is that it doesn't allow for arbitrary data to be sent. Sender and receiver encode the limited information in an agreed-upon way and then it takes a long time, like minutes, to send that little bit of data. Very high redundancy.