This widening gap of support is happening because Canonical themselves do not support these old non-LTS releases
This seems to be a misunderstanding:
According to the very page you linked, 12.04 is supported until 2017-04-26 and 14.04 is supported until 2019-04.
Many users like to have stable operating systems for more than a couple of years and still run bleeding-edge applications on them. The latest versions of Firefox from mozilla.org, for example, still run on very old Enterprise OSes.
Policies like these really make it unnecessarily difficult to use desktop Linux. Please target debian oldstable or CentOS 6; if you do, it will run on newer versions almost automatically; but not the other way around.
Thanks for your consideration!