NixOS. My primary reason for switching was wanting a single list of programs that I had installed. After using ubuntu for 5 years I just lost track of all the tools and versions of software that I had installed…and that didnt even count my laptop. Now all my machines have a single list of applications, and they are all in sync.
Tinkering, really. I did a bunch of stuff with wine and virtualization and troubleshooted across versions. One time I manually updated the version of sqlite in python’s std lib to be a newer version. I picked a non LTS kernel once. All these things compounded and bloated my system. And when I went to do clean up, I didnt have a record of exactly everything I installed, what I used and what I didnt. It was guesswork to clean up my disk or even remember the tools I used to get a project working.
This is solved with declarative configuration, which is the basis of NixOS. I believe VanillaOS 2 has something similar. Likewise, this is one the great benefits of docker, vagrant, ansible, etc.