Who gets the written email warning notice of possible permabanned?

I am really curious how Riot decides who gets an email of possible permaban and who like me, after playing for five years almost daily, dealing with Riot hiccups and slipups, actually spending money in the game for the purchase of Riot points, never cheated, went afk, quit game, threatened anyone, never cheated or used any kind of program or script is permabanned at the end of a game where it was obvious I was set up by a team of people who’s intention was to report people. How is that fair or just?