The thing is… The upgrade path degrades. Once one is 3 or more major versions behind, upgrading becomes technically challenging. (I have done this a few times…) It is better to just reinstall.
That said, a Debian system that works won’t just stop working. My Raspberry Pi 2 has no issues since the initial install.
Professionally, it is better to have a fast recovery path. PXE boot, Debian preseed, a config management system (Ansible, Puppet, etc) and local caches and you can be set in 10 minutes. (After years of setting all of that up.)
Everyone appears to be hitting the “shut up, no one cares”.
There is also the “stop worrying, no one cares.” This is meant to be reassuring. It may be literal.