I am a full stack software engineer, and a project required me to set up a CI/CD pipeline for a project (along with other infrastructure such as package hosting, automated testing, builds, deployments, etc). I'm not a DevOps engineer by title, but I maintain the build pipeline along with other application development tasks.
So, I guess my response would be, "out of need"! :)
So, I guess my response would be, "out of need"! :)