These minor releases are mainly to fix security vulnerabilities. Although WordPress does not officially support these major versions (for new features), they are still being maintained if there are issues to security. (Similar to how Google releases security patches to Android after those devices will no longer receive a new Android version upgrade.)

Right now, NONE of these SECURITY minor releases are being released for the Docker community. Not every site can be directly upgraded to the latest WP major version due to plugin & theme compatibility issues on WP or PHP versions. (Consider production sites that cannot migrate to a new version until they are fully tested and approved.)

Note that those maintained versions should release w/ latest on the same EOL PHP major version (since WP did not drop support for PHP 5.6+ as of today). (e.g. PHP 5.6 -> PHP 7 is a major breaking upgrade, so PHP 5.6 should still be built with (for those minor releases on the maintained WP versions.)

Ref: #399 (comment)