I reckon in most companies, software is written and maintained until the whole system it's a part of becomes obsolete. That typically takes years, sometimes decades if the system is really useful.

It's really risky to rewrite software, so it typically isn't done; it's similar with deletion of code. Most people shy away from it because they're making local changes and don't have enough global knowledge to be brave. So the code lives on.

Personally, in my professional career, nothing I've written has yet been retired or end of lifed, and I've been doing it for 15 years. Some things were experimental and never got released; some things were maintenance for a subsystem that got buried away; but no whole feature nor whole product has been discarded other than by gradual overwriting through maintenance.

This may be true for trivial web apps, but line-of-business software is often used for years, sometimes decades.