Manufacturers (rightly or wrongly) believe users want machines that are as thin and light as possible. This makes a bunch of things more complicated, including

Manufacturers (rightly or wrongly) believe users want machines that are as thin and light as possible. This makes a bunch of things more complicated, including managing system thermals. Heat generated from the CPU has to go somewhere. As you get thinner, it's hard to get as much airflow and so fans are less effective. As you reduce the amount of material in the chassis, the less heat can be dumped in there without it heating up enough to potentially be uncomfortable for the user. Larger internal batteries become another source of heat while charging. Handling all of this safely becomes difficult, especially because there isn't necessarily a policy that satisfies all your users. But you can't leave it purely up to the OS either, because the OS has no idea of what the thermal characteristics of the platform are. So rather than attempting to encode all of this policy directly into firmware, Intel wrote the Dynamic Power and Thermal Framework (DPTF) spec, providing a mechanism for the firmware to share information about thermal control interfaces, interactions, and desired temperature bounds, and then let the OS make policy control decisions around that. Until the OS indicates it's ready to take over, the firmware imposes a default safe policy that's guaranteed to avoid any thermal issues, albeit at the cost of performance. Of course, this only works if the OS knows how to do this, and Intel never publicly documented it so I had to reverse engineer it instead.