Is it just the "retro-computing hobby"? There could still be businesses who might need support for old machines, especially in developing countries. I don't know the actual situation though, I'm open to the idea that my suggestion is insane.
The cost of supporting this old hardware for businesses or hobbyists isn’t free. The parties that feel strongly that new software continue to be released supporting a particular platform have options here, ranging from getting support for those architectures in LLVM and Rust, pushing GCC frontends for rust forward, maintaining their own fork of apt, etc.
There's a non-negligble amount of "handed-down" refurbished hardware from developed to developing. PCs and servers that are already 5+yo and out of market at installation.
(In my second-tier university at my developing country, the Sun workstation hadn’t been turned on in years by the late 2000s, and the the minicomputer they bought in the 1980s was furniture at the school)
Edit: As for big businesses, they have support plans from IBM or HP for their mainframes, nothing relevant to Debian.
See (relatively recent) list of manfuacturers here:
https://en.wikipedia.org/wiki/List_of_x86_manufacturers
and scroll down for other categories of x86 chip manufacturers. These have plenty of uses. Maybe in another 30 years' time they will mostly be a hobby, but we are very far from that time.