Why is 14.04 (Trusty) no longer supported?

On 14.04 (Trusty), the Ubuntu Pro Client package is not receiving upstream updates beyond version 19.6, plus any critical CVE maintenance related to this version.

Version 19.6 already has full-featured support of the applicable Ubuntu Pro service offerings esm-infra and livepatch. In the event that a CVE is discovered that affects the Ubuntu Pro Client version on Trusty, a fix and backport will be provided for those specific issues.