I don't think there is a single type of item in the world for which you could expect it to keep existing indefinitely without maintenance. Machines rust, wood degrades, paintings need restoring every few centuries. And even when properly stored in controlled atmosphere etc, books from a few centuries ago are almost unreadable because the language has changed so much since then (see https://web.cn.edu/kwheeler/diagram_4english.html for example).
Everything in this world needs constant maintenance or it breaks down. Why would you expect software to be any different?