I have software that I need to run for about 5 years. It is certified on Red Hat Linux 6 not 7. I'm not unique. Heck, we had to keep copies of IE 6 running up until a year ago for one testing vendor[1]. I, like a lot of others, need stability and paperwork not new.

Frankly, having a lot of new companies adopting a mantra of "move fast, break things" makes me want to 'upgrade' less and less. I need stuff working at Monday at 1PM for the weekly test offering not some oops.

1) deep freeze or virtual machines are your friend.