[crest]

IIRC because tuning PID controllers for vastly different heating and cooling rates isn't that easy. A CPU can ramp up/down a lot quicker than the cooling system could or should even attempt to react. It's easy to end up with a oscillations the common temperature vs. speed curves (maybe with a hysteresis range) is already annoying enough to tune. Good luck having users come up with good PID terms for their individual combination of parts (CPU, thermal interface, mainboard, case, fans, pump, radiator, etc.).