>and in particular not a sensitive part like kernel error reporting

Things like "kernel error reporting" doesn't exist as discrete element. Sure, you might decide to stop everything and only dump log onto earlycon, but running with serial cable to every system that crashed would be rather annoying. For all kernel knows, the only way to get something to the outside world might be through USB Ethernet adapter and connection that is tunneled by userspace TUN device, at which point essentialy whole kernel must continue to run.