I doubt that i386 is still widely used. You are more likely to find embedded ARM32 devices running Linux, for x86 this is only the case in the retro computing community.
It's actually still pretty heavily used in some niches, which mostly amount to "running legacy binaries on an x86-64 kernel". LWN had an article recently about the Fedora discussion on whether to drop i386 support (they decided to keep it): https://lwn.net/Articles/1026917/
One notable use case is Steam and running games under Wine -- there are apparently a lot of 32 bit games, including still some relatively recent releases.
Of course if your main use case for the architecture is "run legacy binaries" then an ABI change is probably inducing more pain than it seeks to solve, hence the exception of it from Debian's transition here.
Intel Core 2 starting their 64bit CPUs is 20 years old next year. Athlon 64 is over 20 years old... I wonder truly how many real computers and not just VMs there is left.
8.8 percent of Firefox users have 32-bit systems. It's probably mostly people with a 32-bit install of Windows 7 rather than people who actually have an old 32-bit Intel chip like Prescott. Intel also sold 32-bit chips like Intel Quark inside Intel Galileo boards up until about 2020. https://data.firefox.com/dashboard/hardware
People still buy 16-bit i8086 and i80186 microprocessors too. Particularly for applications like defense, aerospace, and other critical systems where they need predictable timing, radiation hardening, and don't have the resources to get new designs verified. https://www.digikey.at/en/products/detail/rochester-electron...
On windows, encountering 32 bit software isn't all that rare. Running on 64 bit hardware on a 64bit OS, but that doesn't change that the 32bit software uses 32bit libraries and 32bit OS interfaces.
Linux is a lot more uniform in its software, but when emulating windows software you can't discount i386
I wasn't discounting VMs with my initial statement. I can totally imagine quite a few VMs still being around, either migrated from physical hardware or even set up fresh to conserve resources.
Plus, keeping i386 the same also means any still available support for running 32 bit binaries on 64 bit machines.
All of these cases (especially the installable 32 bit support) must be as big or bigger than the amount of ARM machines out there.
Few places still maintain genuine i386 support—I don’t believe the Linux kernel does, for example. There some important features it lacks, such as CMPXCHG. Nowadays Debian’s i386 is actually i686 (Pentium Pro), but apparently they’ve decided to introduce a new “i686” architecture label to denote a 32-bit x86 ABI with a 64-bit time_t.
Also, I’m sorry to have to tell you that the 80386 came out in 1985 (with the Compaq Deskpro 386 releasing in 1986) and the Pentium Pro in 1995. That is, i686 is three times closer to i386 than it is to now.
One notable use case is Steam and running games under Wine -- there are apparently a lot of 32 bit games, including still some relatively recent releases.
Of course if your main use case for the architecture is "run legacy binaries" then an ABI change is probably inducing more pain than it seeks to solve, hence the exception of it from Debian's transition here.