Not true. Corporations upgrade their CPUs all the time by the hundreds or thousands. You can see this on eBay and Amazon. Sometimes they will try to sell off large lots of their old used CPUs. Yes, enthusiasts make up a small amount of the market, but it's not only enthusiasts that make simple CPU upgrades. Average Joe consumer has been known to take their computer to a shop and have them upgrade the CPU, or have their geek nephew do it
None of these online computer parts places could survive off of enthusiasts alone. Millions of average people do in fact upgrade their computers, they just aren't considered "enthusiasts".
Also remember millions of PCs are bought online or from local shops that customize computers. Tell them what you want, they buy the parts and assemble it. These are also not "enthusiasts". But with soldered CPUs, the customization isn't as customizable as it is now. Minor issue? Maybe. We'll see.
Then there are the multitudes of people that fry their CPUs and motherboards. Overheating, electrical surges, PCIe slot goes bad, whatever. Why do you now have to pay to replace your CPU when your motherboard dies? Why do you now have to pay to replace your motherboard when the CPU dies? Unacceptable.