I've bult my own PCs for 20+ years, and I can't remeber ever really caring about moving the CPU from one motherboard to another. I shop for them as a matched pair, and assuming they work when I get them, I've alays replace both if problems developed later down the road (because a few years later, when you're on the far side of the failure "bathtub curve", you might as well replace both).
I don't see having to buy the CPU soldered to the motherboard as an impediment really - as long as I can swap out the heatsink and other components.
If your a PC guy over those years you must have had motherboards fail or become flaky, but the CPU to be perfectly fine when you swapped it in to one of your spares? Or even the other way around. You'd probably have a spare board of any socket kicking around right? Soldering down the CPU means loss of this troubleshooting you'd be RMAing the whole board, not just dropping in a spare with the same CPU. If it's out of warranty you'll be stuck with a bigger cost.
It's not just about upgrading and overclockers nervous about bricking a whole board when they roast a CPU, you'd lose that convenience of this kind of troubleshooting.