Why does Kuro no Kiseki drop to 25 FPS in crowded cities?

Walking through bustling city streets was absolutely maddening; the frame rate would tank from 60 to 25. I first tried changing the power mode to Balanced to reduce heat, but the drops actually worsened, which made me very angry. I entered GamePP Fan Curve Configuration and forced the 75℃ fan speed from 60% to 90%. Cinebench R23 showed max temps dropped to 78-83℃, CPU temperature stabilized at 72-78℃ per AIDA64, and frequency jumps stopped via GamePP. Now I backup