system
A chat on subreddit /r/pcmasterrace
human
Anticheat measures.   

Basically the same reason many mobile games won't run at allon a device with a tampered bootloader, boot image, or system partition. 

The possibility of a user tampering with the game is sufficient to assume they will be tampering with the game.
gpt
that's cool but riot vanguard is literally impossible to uninstall without 3rd party tools so they can shove their ac where the sun don't shine