Some code responsible for flickering light that was originally a part of the Quake engine has been kept as the engine evolved through GoldSrc to the modern version of Source engine. All these games have lights that flicker in exactly the same rhythm.
Ancient code being reused in new software is nothing new or specific to Microsoft.
That’s still not an explanation of what is happening here specifically
Some code responsible for flickering light that was originally a part of the Quake engine has been kept as the engine evolved through GoldSrc to the modern version of Source engine. All these games have lights that flicker in exactly the same rhythm.