It’s fun. Lots of people like doing retro game dev and the like, but often you are stuck with ancient C toolchains that suck even if you like C itself. Getting Rust working is a great way to make it more enjoyable from a hobbyist perspective, I think.
If you talk to the spooky GCC people with beards they'll point out that they support much much weirder chips than that (albeit with little to no library support).
You may not believe me, but there are relatively modern 386-compatible embedded systems. Some of them run DOS for the sake of very old applications, such as certain industrial control software. Targeting them for modernization without gutting the hardware (which can be perfectly functioning and highly durable) is a valid goal.
You're a cat, a 386 DOS machine is a tiny box on the floor. You jump in the box and slowly settle all of your limbs into the box till you can sit. Now you fit.
Perhaps the same kind of people who got GCC to compile for 386 DOS machines (also using DPMI). Which might sound useless, since it's an underpowered operating system running on underpowered hardware, but it was used to build some very popular software, like the original Quake game (source: http://www.delorie.com/djgpp/history.html).
The FastDoom port slims down some floor textures and such and makes Doom playable (and not stamp sized) on a 386.
About the 386, you could run SICP as a GNU Info file blazingly fast and a Scheme compiler on another TTY, or under GNU Screen.
You could typeset with Groff and Mom, too.
Now try running LaTeX on that. Yes, Donald Knuth is the Ur-creator on CS and typesetting, but hey, sometimes you don't need a full 3GB Texlive suite to typeset some book or math equation notebook.
I don't know why I laughed so hard at this. Why would any sane person do this?