You answer your question yourself with
in fear of breaking something and having to reinstall (and losing something in the process)
Version upgrades are a big thing and unexpected things can happen. Would you be a happy user if the system auto updated to the next version and something truly broke? By forcing manual upgrade they can better inform users about possible unexpected things, and e.g. advice to do backups first. Thus users would be more prepared for this. Also version upgrades take a lot longer time than normal updates since it has update all packages, do other changes to the system etc.
Have ran into the same problem at some. Try running btrfs balance on your drive. Both metadata and normal data. It won't delete anything. On my phone so grabbed just q quick linking https://commandmasters.com/commands/btrfs-balance-linux/.You need to run it bit by bit (see the filters).