To comment on "Where do people like network engineers learn how to configure Cisco routers and use whatever config software they use? Where do sysadmins learn B

To comment on "Where do people like network engineers learn how to configure Cisco routers and use whatever config software they use? Where do sysadmins learn Bash, Unix, backup management etc?" - they certainly can do at university courses. Just as universities offer study programs and degrees in software engineering, there are also programs and degrees for network engineering, which would include not only the theoretical basis of networking but university courses for applied networking where they would learn all that you describe and much more; a university teaches a network engineer to configure routers and manage backups just as they teach a first year electronics engineer to solder stuff. Sure, a generic computer science or software engineering program will not include these courses, that's a usually a separate specialization, but universities definitely do offer engineering programs.