You can design hardware that's capable of dissipating the maximum heat output of every component simultaneously, but you'll end up with hardware that's significantly larger, heavier, and costs more to manufacture. Or you can design hardware that's capable of dissipating the expected heat output under a range of use-cases, and devolve policy management to the OS so it can (based on user preference) prioritise appropriately, allowing you to produce smaller, lighter machines that either cost less or generate more profit. Even if the motivation for cutting costs is to increase profit margins, users generally still seem to prefer the smaller, lighter hardware that works just fine under most circumstances.