Yes, encryption would make some enforcement actions slightly harder, but we tolerate it in plenty of other settings where you have a constrained, shared resource. Wifi comes to mind. Nobody gets upset that you can't examine your neighbors' packets to make sure they're following the law or not using the spectrum for a purpose other than "bona fide" home wifi. Even though the wifi spectrum in urban areas is far more crowded than ham frequencies.
For much of the hobby's history, the government was deeply distrustful of amateur radio. They flat out banned all operations during WWI and WWII. And a lot of ham radio folks reminisce about the good old times when the government had listening stations and amateur radio enforcement operations throughout the country, and would knock on the doors of any amateurs who did anything wrong. Well, they funded that not because they shared your passion, but because they wanted to keep Soviet spies at bay.
The ban on encryption was supposed to serve the government's interests, nothing more. If you worry about corporations misusing the spectrum, it's sufficient to require identification in plain text; if somebody is using amateur callsigns but sending 9-to-5 chatter on a fixed frequency every day, and you pinpoint it to a local warehouse, that's more enough for enforcement action, right? Except... there is almost no enforcement these days, because the Cold War is over and the government lost all interest.
Ham radio getting "banned in unstable countries" seems like a whimsical concern, too. First, many other countries do not restrict encryption the way US does. Secondly, in the era of the Internet, mesh networking, ubiquitous smartphones, etc, ham radio hardly registers on the radar for most governments. Maybe in North Korea... so let's ban encryption domestically, including in the short-distance VHF/UHF band, to stay on Kim's good side?