Likely a simplified view, actually. All sorts of hardware tuning parameters are exposed to software, including numerous settings around things like memory timings and maximum CPU wattage. The hardware uses this for automatic control independent of the OS (you don’t want an out of control system using 100% of the CPU to also not be telling the fans to spin up).
The delta between minimum and maximum power consumption has gone up considerably over the last ten years, as more and more focus has been put on mobile devices and computing. Likewise, the complexity of these controls has increased. Nowadays, the CPU is tuned for the computer it is put in (including, across ultrabook models, having the same processor run at different base clocks depending on the cooling/power capabilities of the system)
Intel chips can run very fast if not for those excess power and excess heat problems - they have surpassed the heat density of a fission reactor at max usage. So they now have a numerous dynamic adjustments, such as a base clock and ‘turbo’ max frequency. - the system can draw more power and run faster to finish tasks faster. But this generates heat, and can only be used short-term.
I expect Apple’s firmwares were for whatever reason (oversight on the release process?) were not limiting the power draw properly, causing systems to critically overheat. Then, the hardware throttles them down in an emergency mode until the heat dissipates - then more than likely, max draw again for a short period of time until the next overheat cycle.
Its not just the fans, because the system components (including the CPU itself) just aren’t designed to permanently operate at turbo speed.
Simplistic analogy time - it’s like the old NES game Excite Bike - if you just hold on the accelerator, your bike will overheat and you will just sit on the side of the track for a while. The new firmware tells the laptop to take its foot off the accelerator before that happens.
