I think services take me literally half an hour a month or so to deal with unless something major has changed, and a major K8s version upgrade where I roll all nodes is a few hours.
If people are deploying clusters and not touching them for a year+ then like any system you're going to end up with endless tech debt that takes "significant planning" to upgrade. I wouldn't do a distro upgrade between Ubuntu LTS releases without expecting a lot of work, in fact I'd probably just rebuild the server(s) using tool of choice.