They back-port "high-impact" bugs such as security issues (your example), severe regressions and bugs causing loss of user data. They do not back-port other bug

They back-port "high-impact" bugs such as security issues (your example), severe regressions and bugs causing loss of user data. They do not back-port other bug fixes or new features. The result is that you often find the version included in your Ubuntu release is stale. See https://wiki.ubuntu.com/StableReleaseUpdates#When https://wiki.ubuntu.com/StableReleaseUpdates#When