Microsoft Office still exists, and can still open Word / Excel / etc files from 25+ years ago.
Adobe Photoshop still exists, and can open PSD files created 25+ years ago.
Microsoft Xbox One X still exists, and is backwards compatible with titles from the OG Xbox release, as far back as 22 years ago - https://www.xbox.com/en-us/games/backward-compatibility?cat=...
Microsoft Zune (launched 2006) is still supporting and fixing compatibility issues, all the way up through Windows 11 now 17 years post-launch - https://www.pcgamer.com/microsoft-just-fixed-a-zune-compatib...
Warframe (Canadian MMO-lite third-person action video game) still supports every purchased piece of digital content ever sold, on all platforms, from the very first purchase, over the past 10 years. (I believe the same is true for Final Fantasy 14 which launched in the same year, but I'm less familiar with that one)
Vanilla accounts from World of Warcraft (now 19ish years old) still work and function today.
---
I don't think anyone expects things to last forever. I think they're just expecting things to last longer than "a few years", and there's no technical reason why we couldn't ensure that.