Why does my PCCOOLER RZ820 throttle Civ VII CPU speeds?

I was frustrated when my Civ VII turns took 15 seconds instead of 2. I tried maxing fans to 2000 RPM, but it was noisy and ineffective. I used GamePP Fan Curve Configuration to set 70C at 1500 RPM and 80C at 100%. AIDA64 showed temps dropped to 78-82C and frequency held at 5.0-5.2GHz, making the game stable again.