Why the Ubuntu 16.04 LTS is till 2020-2022 and not just 2022?

The command ubuntu-support-status shows that the majority of the packages on my Ubuntu 16.04 are supported until April, 2021 which is the same as the Ubuntu 16.04 release end of life which is listed at the official Ubuntu release cycle | Ubuntu website. In Ubuntu 20.04 and later the command ubuntu-support-status has been replaced by the ubuntu-security-status.

Example results of ubuntu-support-status in Ubuntu 20.04:

$ ubuntu-security-status
1670 packages installed, of which:
1601 receive package updates with LTS until 4/2025
  69 could receive security updates with ESM Apps until 4/2030

Enable Extended Security Maintenance (ESM Apps) to get 0 security
updates (so far) and enable coverage of 69 packages.

This machine is not attached to an Ubuntu Advantage subscription.
See https://ubuntu.com/advantage

As you can see on the chart on the linked website (part of which is shown below), Ubuntu 12.04 LTS has already been an end of life release since April, 2017, but its security maintenance has been extended for an additional 3 years until April, 2020 for Ubuntu Advantage customers, and the security maintenance of Ubuntu 14.04 has been extended for an additional 3 years until April, 2022.

After the period of security maintenance has ended you can still continue to use the end of life Ubuntu release, but it will be less secure because it will no longer be updated.

Extended Security Maintenance (ESM) is free for personal use on up to 3 machines (limitations apply). All you need is an Ubuntu One account. Initially, free subscription is available for Ubuntu 14.04 LTS only.

The next Extended Security Maintenance (ESM) release after 14.04 will be Ubuntu 16.04.

At OpenStack Summit held on November, 2018 Canonical and Ubuntu founder Mark Shuttleworth said in a keynote that Ubuntu 18.04 Extended Security Maintenance support lifespan would extend Ubuntu 18.04 support from 5 years to 10 years.

There are some packages installed on my system that are supported only until April, 2019 and other packages that are supported until January, 2023, however like the other Ubuntu LTS releases Ubuntu 16.04 LTS is supported for 5 years after its release date.

Ubuntu Core, with an image size of 260MB, is the smallest Ubuntu release to date. This makes it ideal both for IoT devices and cloud containers. Ubuntu Core 18 is based on Ubuntu 18.04, and is supported for 10 years. A new release of Ubuntu Core is released every 2 years on even numbered years (2016, 2018, etc.).