What is it used for?
If you buy Intel, you know beforehand you won't be able to upgrade the CPU, since the socket is changed (intentionally, of course) every generation. But the CPU isn't the issue for e.g. gaming, and upgrading every generation or every other generation largely doesn't make any sense at all with Intel parts for the last eight years or so.
Since you're saying obsolete, you probably bought into 1150/Haswell. It was known this was the last pure DDR3 platform, but you can still get DDR3 memory new, if you need more. So that's not a problem, really. (And it's actually cheaper than DDR4 memory)
Graphics cards can keep up for years nowadays. I've used a midrange-highend card for five years before upgrading; I could still play new games at mid-to-high settings. Graphics cards can always be upgraded in any computer (if the PSU has enough power, which is rarely an issue).
Is it really true that the socket changes every generation? My impression was that sockets changed every 2-3 generations, not every one. Not that that entirely defeats the point, but it expands the window.
Intel seems to change desktop sockets every 2 years now. That includes multiple generations, but 2 years of CPU improvements is not significant in almost all cases. A new motherboard with each new CPU is the likely situation. AMD has supported sockets for longer, and that seems to be continuing.
I can at least upgrade the SSD and GPU without throwing the whole damn thing out, but even then it's hard to justify.
I agree with the ssd, tho. The newer PCIe based ones in the m.2 formfactor areso much faster it feels a bit like a waste to buy a sata SSD.
Aren't the Vegas quicker, and the NVIDIA offering has been improving quite a bit over the last 2 years? I might not be paying enough attention, but I'm pretty sure the 1080 ti and 1070 ti's came out only recently.
If you upgrade the CPU, you usually have to upgrade the motherboard. That's about it.
How is that at all possible unless it was under powered in the first place? Maybe it can't play some of the latest titles at max settings but a 4 year old machine should be able to run just about everything decently.
What's stopping you from upgrading the graphics card? Looks like plenty of high end cards have PCIe3 support. RAM can always be upgraded, though few games will makes use of the 8GB that was pretty standard in gaming PC's nearly a decade ago. A new CPU won't gain you much gaming wise.
Most games target PS4 level specs anyway, which is now a 5 year old machine.
Unless you got a bulldozer CPU, I don't believe you. I bet that upgrading just the graphics card would give you 90% of the effect of upgrading everything.
You can upgrade your storage independently, you can upgrade you GPU out of step from other components, you can upgrade GPU more often than CPU without compromising too much. And so on. You can for example keep your soundcard since 10 years ago with some fiddling with drivers. One of my SSDs is 6 years old and while not ideal case it is still much faster than modern HDD and I use it constantly.
What you also mention - case and PSU - those alone cost ~100-200$ each, so worthy saving for upgrade. My seasonic PSU will work for a decade at least, or more.
It is not easy, yes. But possible.
Upgrade the RAM at the start of a new spec and you'll be fine. CPU/mobo go hand in hand, but you're rarely going to need to upgrade that anyway.
Turns out in practice technology changes enough over that time to only leave the case, and perhaps the PSU. The motherboard, CPU, RAM and graphics card are all obsolete now. The SSD can be reused but newer technology is much faster.
I don't know what gets saved by upgrading parts rather than the machine. The same amount of electronics are disposed of (or sold on the second hand market)