Military service isn't popular at all, but the majority of people do agree that it's necessary to have a military and they don't want a professional army. So that leaves the current system.
The popular mechanism remains- there's no need to encourage a voluntary interest in military culture and therefore military readiness, when it's already a popular idea to mandate the readiness.
In the absence of that mandate, there would be a vacuum in which citizens suddenly have self-interest in promoting voluntary readiness, which is implemented culturally.
