Your reality does make better sense, but doesn't make a good story.
I’d hazard a guess that 8-bit machines played a part in the author’s young life - first computer, first job, happiest childhood summer, last computer they felt in control of before they got annoyingly complex - something like that. And therefore a collapse ending right when the author would have useful skills but things wouldn’t be too hard, is the most fun one to imagine.
Computing was around 40 years before the 1980s and electricity for a hundred years, but who wants to try and rebuild room sized punched card machines for ballistic trajectory calculations, get greasy fingers on mechanical parts, or deal with HT electrical power supplies safely, yawn, no fun there. rPi the same - by then everyone can do it and author isn’t special, so whatever. It’s not different enough from right now.
¹ "logic gates" not necessarily being transistor-based, either; one could take a cue from the guy building a 32-bit RISC-V machine with vacuum tubes: https://www.ludd.ltu.se/~ragge/vtc/
I'd guess that those 8500 transistors would be better used to build thousands of much simpler logic controllers to help automate infrastructure that's lost its computer control systems.
https://en.wikipedia.org/wiki/Transistor_count
There are simpler "transistor computers" that might be more feasible to build from discrete components:
https://en.wikipedia.org/wiki/Transistor_count#Transistor_co...
[1] https://en.wikipedia.org/wiki/ARM_architecture#Acorn_RISC_Ma...
says about 30.000 gates, which is 10.000 less than Motorola 68000 and arguably faster.
[2] https://en.wikipedia.org/wiki/Zarch
at least made us Amiga and AtariST geeks envious.
Furthermore there is 'Microsequencer' like described there:
[3] https://en.wikipedia.org/wiki/Microsequencer
and following up from there to for example
[4] http://www.microcorelabs.com/mcl65.html
which is a 6502 softcore with microsequencing applied
Alas... There are many options to choose from according to the available technology, tools & knowledge. One does not have to make an exact copy of something which made sense for arbitrary reasons, which don't necessarily apply when doing it from scratch under different circumstances.
