US-CERT on the August/September 2018 ATM hacks which affected several nations:

(…) all of the compromised switch application servers were running unsupported IBM Advanced Interactive eXecutive (AIX) operating system versions beyond the end of their service pack support dates;

This is the typical example of short-term thinking. Someone/some comittee decides not to spend on a supported version of a particular software, but don’t consider what the downside could be.