I'm sure the other CMS are fine but I want my site to auto update itself and all its plugins for the next 20 years with me hardly touching it.
Reality of that is that most people will use some plugins or their theme wont update or your code will have breaking change.
The auto update is nightmare. Because so many people are trying to hack WP you gotta do it and every other update becomes stresfull event. Good luck updating someone elses plugin.
Much higher chance of website working 20 years is - take simple preferably file based system. Make manual update every 5 years. If its good system then the migration will be well documented and painless probably taking 5 minutes.