[RadioAstronomer]

IIRC, you recently explained the reasoning behind this. Isn't it both because narrowband CW is not found from known natural sources, and because it is found from known intelligent sources (human-made radio stations)?

You are most correct! :)

[apochromat]

Narrow band? Hmmm.... Perhaps unfortunately for that approach, spread-spectrum may be a superior CW for many reasons, including efficient channel sharing and space-time signal demodulation i.e. turning multipath from a disadvantage into an advantage.