If you write a commercial program and sell it once, you are probably not going to be selling new copies in 10 years. If you keep getting paid you should indeed keep working. But if you stop working on it, it is better for the finished software to last longer.
Windows 11 has a "compatibility mode" that goes back to before XP. Android has a dialog that says that an old APK "needs to be updated", regardless of the continued existence of the original developer or whether the user is happy with the features and level of support.
It is this attitude of "we don't need to think about backward compatibility because we are powerful and all software has a developer on call to deal with our breaking changes" that causes software to go obsolete very quickly now. User needs also change over time, but not nearly as fast.