The basic case: Alice wants to talk to Bob and would rather not have their crazy neighbor listen in and threaten violence because psychosis (Don't believe me? Hang out on the fun parts of the HF spectrum).
The public service use case: a disaster occurred, I need to send medical information to a known recipient. Other countries have allowances for this but the US does not.
The because it's literally unenforceable anyway case: yeah, go after noise sources that don't have an ID but prove to me my shitty CW transmitter with a trillion ppm of phase noise isn't actually broadcasting encrypted PSK within pulses.