If my phone or laptopbattery dies on me I could lose a lot more time/money than by simply not wasting precious resources like battery charge. People buy devices for specific needs. If they can't meet those needs the purchase is a net negative.

I would argue that there is a lot less useful work available to run per unit available CPU time than there is time.

Otherwise, there would be market for people to sell their spare CPU cycles.

The only entities selling CPU cycles are big cloud providers who have much higher utilization in general.