Software is written against APIs, not years, so the problem with this sort of thinking is that software written -say- 10 years ago might still be using APIs from more than 20 years ago, so if you decide to break/remove/whatever the more-than-20-year-ago APIs you not only break the more-than-20-year-ago software but also the 10 year old software that used those APIs - as well as any other software, older or newer, that did the same.
(also i'm using "API" for convenience here, replace it with anything that can affect backwards compatibility)
EDIT: simple example in practice: WinExec was deprecated when Windows switched from 16bit to 32bit several decades ago, yet programs are still using it to this day.
Pretty much the only 16-bit software that people commonly encounter is an old setup program.
For a very long time those were all 16-bit because they didn't need the address space and they were typically smaller when compiled. This means that a lot of 32-bit software from the late 90s that would otherwise work fine is locked inside a 16-bit InstallShield box.
> Pretty much the only 16-bit software that people commonly encounter is an old setup program.
I know quite a lot of people who are still quite fond of some old 16-bit Windows games which - for this "bitness reason" - don't work on modern 64 bit versions of Windows anymore. People who grew up with these Windows versions are quite nostalgic about applications/games from "their" time, and still use/play them (similar to how C64/Amiga/Atari fans are about "their" system).
