Because there's standardisation beyond just where the app/server/whatever is going to run in production - having a standard way to spin up, describe and control applications & their dependencies that works cross OS lets developers & devops speak the same language, with the same commands.
Is docker the silver bullet for this? No, there's tons of other options. But "everyone should use Debian and Fedora" isn't a realistic standardisation.
Is docker the silver bullet for this? No, there's tons of other options. But "everyone should use Debian and Fedora" isn't a realistic standardisation.