Some examples of config files that are not KEY=VALUE: Apache, X11, resolv.conf, sudoers, syslog.conf, mtab, inittab/gettytab, ntp.conf, passwd/group/shadow, lda

Some examples of config files that are not KEY=VALUE: Apache, X11, resolv.conf, sudoers, syslog.conf, mtab, inittab/gettytab, ntp.conf, passwd/group/shadow, ldap.conf, PAM, openssh, CUPS... just a few on my desktop. These files support a wide variety of functionality beyond what a data-serialization format like YAML support. The functionality is designed for humans to input data germain to the configuration of the application in an easy way. That is to say, it both makes the admin's job easier, and tells the program what it wants to know. Data serialization formats (JSON, YAML) are particularly poorly suited for configuration. JSON doesn't even support comments. YAML does, but then forces you to correctly format the document in a non-human-intuitive way, making the admin's job harder, and not necessarily telling the program what it wants to know. It has been well established how many problems humans encounter editing YAML files, to the point that people just take out features to make it less problematic, though of course some problems remain. They could eliminate these problems by using an established robust configuration format, or even making up their own, but modern programmers have a poor education in software design and avoid anything that isn't trendy or popular. .INI is a decent enough format, with the caveat that it was never a standard, so parsing is always application-specific. At that point you might as well just make your own configuration format that serves the admin and programmer better than trying to force complex configuration into simple KEY=VALUE pairs. XML is sometimes actually useful, but time has shown that it is not human friendly, and often not even program friendly.