Nothing is free - everything is a trade off. Hardware isn't magical. There is cost to how fast you can switch between various C states on Intel CPUs for example

Nothing is free - everything is a trade off. Hardware isn't magical. There is cost to how fast you can switch between various C states on Intel CPUs for example. There is hardware that explodes if you play too hard for another example. Servers need maximum performance and low latency - guess what aggressive power management will do to that? You talk about drivers but what about firmware? Have you looked at how kludgy and unreliable ACPI implementations across hardware are? What about the in kernel drivers being mostly reverse engineered - how many hardware vendors care to provide power management docs for their hardware? Everything is possible of course - it's just that it is way harder to do when you support everything from toasters to big iron in case of Linux and Phones to gazillion varying PC hardware combinations in case of Microsoft.