Why does my CPU throttle in late-game Civ VII?

I was stuck in a late-game Civ VII match with 50+ cities, and the CPU load spiked to 95%, causing the PCCOOLER RZ820 to fail. I tried manually maxing the fan to 2000 RPM, but the noise was unbearable and it only dropped the temp by 3C. I used GamePP Fan Curve Configuration to set 70C to 1500 RPM, 80C to 100% speed, and a low-load limit of 600 RPM. AIDA64 confirmed core temps stable at 78-82C and frequency holding at 5.0-5.2GHz, which saved my turn times from 15s to 2s.