The difference is that the average distro user cannot just push a new ISO image to the mirror network, say after changing some installer defaults (or more reali

The difference is that the average distro user cannot just push a new ISO image to the mirror network, say after changing some installer defaults (or more realistically, push a new QCOW2 image). There's also a substantial delay between mirror pushes and the update being ready for installation everywhere, something that developers probably would not accept in their pipelines.