In short, why do you have this interest that we all seem to share? The details aren’t important. What I’m assuming we all share is an interest in what might be considered non-mainstream computing. Weather it is reproducing the computers of the past, improving them with modern components, or using 6502s in FPGAs, the common ground is there.
I will attempt to answer my own question. For me there are three angles that drive this interest:
1. Since about the mid 90s computers have become impossible (for me) to completely understand, top to bottom and left to right. I pretty much knew the Sinclair Spectrum completely. It was possible to understand exactly how it worked. I almost had the same relationship with my Amigas. It was certainly possible to understand those machines completely, both hardware and software, and many people did. It is not possible (for me) to do that with modern computer systems. Things are hidden, details obscured, or there is simply too much to know. In building my own microcomputer I can again use a system I completely understand. Every software routine I write, every part of the circuit (including stuff in HDL) I know what it does and why it is there. I find this compelling.
2. The challenge of producing a working computer system of my own design. The fact that is not useful to others does not matter. I still consider it an achievement. It is a fun and interesting hobby, which is what hobbies are for.
3. Since starting out about 2 years ago, I have laid out reasonably complex PCBs, got much better at soldering, learned about SMT, revisited digital logic design, and learned VHDL, something I managed to miss out on through my university studies 20 years ago. I’ve also learned a lot about microcontrollers. Most of these things are current skills with value.
I’m very interested to learn other peoples thoughts. Are you motivated by the same kinds of things? Is there a real practical angle? Maybe you are actually making real products? Perhaps the computers you've built are doing actual useful work?
Apologies for the strangeness of this question. I’ve just been curious to know if maybe my situation is unique? I’m guessing it isn’t but it would be great to hear other people’s perspectives.