They could remount it read-write, but they don't. If systemd had made a unilateral change that broke existing userspace people would have been unhappy for a dif

They could remount it read-write, but they don't. If systemd had made a unilateral change that broke existing userspace people would have been unhappy for a different reason. Doing this in-kernel means that the issue could be fixed without breaking existing userspace, so it's clearly the better solution.