I think the answer is that CPU time doesn't have consistently high value to the CPU owner, and isn't a free market as CPU time is non-transferable due to securi

I think the answer is that CPU time doesn't have consistently high value to the CPU owner, and isn't a free market as CPU time is non-transferable due to security concerns. It isn't practical to buy compute power from a diverse set of CPU owners, because any of them may be malicious, and this problem only increases with scale. The only exceptions are cases where you can afford or mitigate malicious CPU owners, which doesn't lend itself to general computing.