This is just educated guesses, it's surprisingly difficult to find context and history of (granted, fairly obscure to begin with) regulations and why they are what they are and when they were implemented.
Ham requires you to identify your transmissions with your call sign periodically, if that's encrypted it's more or less impossible for anyone but those who have the key to decode.
Ham is a "public interest" kinda service, so the ability for the public to listen to transmissions is a big part of the spirit of why the ham spectra was carved out rather than sold for private use. For example, a business could use encrypted ham to conduct business (also prohibited) and no one monitoring would be the wiser, even if the protocol included plain-text station identifiers in the data stream to be compliant with the station ID requirement.
More speculative, cold war era paranoia about subversive groups using encrypted protocols on ham bands to coordinate terror attacks, relay espionage information, and such was probably a factor.
This is just educated guesses, it's surprisingly difficult to find context and history of (granted, fairly obscure to begin with) regulations and why they are what they are and when they were implemented.
Ham requires you to identify your transmissions with your call sign periodically, if that's encrypted it's more or less impossible for anyone but those who have the key to decode.
Ham is a "public interest" kinda service, so the ability for the public to listen to transmissions is a big part of the spirit of why the ham spectra was carved out rather than sold for private use. For example, a business could use encrypted ham to conduct business (also prohibited) and no one monitoring would be the wiser, even if the protocol included plain-text station identifiers in the data stream to be compliant with the station ID requirement.
More speculative, cold war era paranoia about subversive groups using encrypted protocols on ham bands to coordinate terror attacks, relay espionage information, and such was probably a factor.