Not all software can be sufficiently insulated from external changes, but almost all software I care about can be. My normal update cadence is every 2-3 years, and that's only because of a quirk in my package manager making it annoying for shiny new tools to coexist with tools requiring old dependencies. The most important software I use hasn't changed in a decade (i.e., those updates were no-ops), save for me updating some configurations and user scripts once in awhile. I imagine that if I were older the 18yr effective-update-cycle would happen naturally as well.

My gut reaction is that the software you're describing relies heavily on external integrations. Is that correct?