At some point it makes sense to update even if the content itself is "complete": supporting newer screen resolutions natively (instead of going with some kind of fallback behavior), making sure all the outdated and long since sunset 3rd party SDK calls don't cause crashes etc.

Also if you managed to build, prepare (App Store metadata in different resolutions etc), submit and finally get your app shipped to the end user that was no small feat a couple of years ago. Probably not a very useful skillset to have if you only do it very infrequently (read: waste of time).

Requiring additional screenshots, icon sizes, universal app (iPhone+iPad, also supporting split view), new copy for different types of meta (e.g app sub title) for all the locales you probably had translated externally at some point, new privacy guidelines etc.. all not very attractive to get into even if not forced to update like this, especially if you lose your ratings in the process.