i386 (32 bit) only processors we discontinued but 64bit processors can operate in 32bit mode so toolchain was still widely available and there was still demand for i386 OS that would run on modern hardware in i386 mode for some ancient software.

Yeah, and you can still run i386 binaries on widely available amd64 CPUs. So this is an even stronger argument for killing these other obsolete platforms.

You can only run the binaries if you have the libc to run them.

You say that like it is a higher or even comparable barrier to having alpha/m68k/sh4 hardware; it isn't.

Uh? I don't understand what you're saying.

The actual Intel 80386 processor was discontinued in 2007, but the i386 architecture -- ia32, 32-bit x86 -- lived on for longer in the semi-mainstream (there were 32-bit Intel Atoms introduced to the market as late as 2012, AMD Geodes were sold until at least 2019, and I believe some VIA C3/C7 derivatives made it into the 2010s as well) and is in fact still in production to this day for the embedded and industrial markets (Vortex86, etc).

All of those are i586 or i686 though right? AMD Geode LX is the only i586 CPU produced in the last 15 years.

Everything else is at least i686 and Rust has perfectly adequate i686 support.

Is there any major distro left with pre i686 support?

Debian's i386 is actually i686 I believe.