Why does my CPU throttle in the underground facilities?

I felt absolute dread when entering the slime-filled underground facility; my chassis fans surged violently while the game stuttered. I tried limiting the maximum processor state to 99% in Windows power settings, but while temps dropped by 5°C, my minimum FPS plummeted from 45 to 32 per RTSS. I then used the GamePP Fan Curve Panel to force an 85% fan speed whenever temps hit 75°C. After this, AIDA64 showed initial spikes of 82-89°C dropped to a stable 68-74°C, and GamePP Benchmark confirmed fans stayed at 1200-1400RPM.