You can also use backports for some of the more “system entangled software” that cannot be packaged in a flatpak. Or, you can skip ahead to “Trixie” unstable. It has been great for me for the last several months. It’s arguably more stable than what Ubuntu calls an LTS.
It exists because, long ago in a galaxy far far away, a sysadmin ran out of space on a drive. The system was split between two 10MB(?) drives, one was / and one was mounted at /usr, for User data. They moved some of the programs to a folder for a dummy user, /usr/bin, and put that in everybody’s PATH.
Everybody kept on doing things that way ever since. Social momentum is funny that way.