your normal distro does updates by pulling every package on your system and swapping files mid running this can cause miriad of issues just by doing it and another miriad if update is stopped mid updating(not always but sometimes). So this means your system is being recomposed at runtime

while on other hand on bluefin and simialr image based OS-s composition of your OS is done somewhere else not directly on your running file system(could be your computer just not your rootFS) then it takes that image and pulls old image(normally on startup) and places new one in its place all in one go, so any composition errors dont get triggered during update and such. (composition before deployment is a principle cloud-native pushes) This makes updates far more stable and less error prone and automatic updates are a thing you dont even notice day to day. and what happens if image cant boot it just boots the old one or you can select the old one from grub(2 old versions are stored per default if i remember correctly) This idea has been successfully used by likes of android chromeOS and such to create seamless and risk free updates.