Perhaps not one key event, but a combination of solid state storage removing the hard-drive-failure event that often drove people to upgrade, CPU performance topping out, and RAM well beyond anything most programs need have all conspired together to give us desktops, laptops, and mobile devices that basically no longer get 'old'. Not to mention that power consumption is low enough now that PSUs just aren't burning out like they used to :-).
Something strange happened in the last year or two. I buy computers all the time for DragonFly testing, so I have a pile of machines of all different kinds including a bunch of BRIX form-factor units. I stuff nominal sweet-spot memory and storage into them all, always, because they get repurposed or farmed out to friends all the time to make room for new hw.
The strange thing that happened... it became convenient to just throw 8-16GB of ram into all of these things. Even the tiny little BRIX. And even the little BRIX can dual-head two 4K displays, and easily fit a 2.5" SSD (and so can hold quite a bit of storage). None of these boxes have any moving components except a fan or two. They don't fail if I put them on a shelf for a year.
Up until about 2 years ago I was regularly throwing away my oldest hardware, including the bulky cases (which had to be large enough to hold a CD and/or DVD and several 3.5" drives).
But the remainder of that really old hardware petered out last year. Now there's no reason at all to throw away my 'new' old hardware... it is still useful enough that I can give it away or repurpose some of its components. The cases are all small so I just reuse those if I can't find any use for the mobo. I reuse the SSDs (I never reused old hard drives). I reuse the PSUs (if any). There's no graphics card to replace since it is built into the cpu.
In fact, the only thing I haven't been able to recycle in the new old machines have been the DIMMs due to continuous technology changes, but those just stay with the original motherboard.
In our colocation for DragonFly our blade server (12 x haswell blades in 2U) has handled all of our needs and other than slowly replacing the remaining HDDs with SSDs will probably handle all of our needs for the next 10 years. Or longer. It will be interesting to see what the failure mode is for the hardware because it will probably be the first piece of hardware I own that stays fully active and relevant until the blades actually physically fail.
I love the technology but I think there's only more pain to come for Intel.