Is it because they have a 32-bit CPU? Is it because they have a 32-bit OS on a 64-bit CPU? Are they running a 32-bit Python on a 64-bit OS?
first, answering the question (TL;DR - despite this we can shift it down to tier-3 for 3.13):
(1) Because 32-bit applications are still supported on Windows and some people may be using embedded Python to interface in-process with those. The case of embedding Python in an extension to one such application came up in another conversation recently IIRC. People needing embedded Python require a Python that matches. But I assume embedders are also more likely to be people capable of doing their own builds.
(2) Do understand that Microsoft only stopped allowing OEMs to ship 32-bit Windows 10 in May of 2020. Before then some still were on lower end system configurations usually with <=8G RAM. It had nothing to do with what the CPU itself supports (the last 32-bit-only x86 was ~15+ years ago). Those shipped-with 32-bit windows 10 computers still exist. Users are usually not aware and won’t figure out how to upgrade without being forced to. BUT their number seems few (good, because i think they no longer get security updates?):
Per Dropping 32-bit packages - #13 by hugovk in May this year Hugo found that PyPI downloads for Windows numpy were <2% 32-bit x86, and if you focus on recent >= 3.10 Pythons only - the number was < 1%.
That is reassuring!
So we should be able to stop considering 32-bit x86 in 3.13 a priority (kick it down to tier 3 if we’ve still got a buildbot). That’d put it in the same category as arguably much more important to the world, tier-3 aarch64 (arm64) Windows.
PEP 11 – CPython platform support | peps.python.org would need to be updated to mention this change for 3.13+.