Why does Avowed downclock and drop frames after long sessions?

My Gloway Celestial Strategy DDR4 3200 hit 85℃ in Avowed, triggering automatic downclocking and frame drops. I tried setting fans to 100%, but the noise was unbearable and it only dropped temps by 2℃. I used GamePP Fan Curve Configuration to set the acceleration trigger to 70℃ and replaced the thermal paste. AIDA64 stress tests showed core temperature reduced to 72℃, with fan speeds stabilizing at 1500-1800 RPM. The performance degradation stopped completely, and I could play for hours without the discomfort of sudden frame rate collapses or excessive heat.