The thing that a lot of people don't understand is Riot at the end of the day is a public for profit company. Even if Riot was able to create an AI system which was capable of immediately identifying players in violation of the rules with 100% accuracy it makes zero sense for the company to dish out punishments that would leave them with a net loss with their player base and thus less potential revenue.
So knowing this it should shed a lot of light on why things are the way they are. Riot does not want to ban you, punish you or anything more than they absolutely have to to keep the player base under control. They ban bots, and cheaters because they ultimately greatly reduce the confidence real players have in the system and from plenty of other games they know people would leave if this got out of hand. They ban really toxic people because they know if they let them stay, their toxicity would eventually lead to others quitting and would ultimately lead to a net loss in revenue.
Riot does not want to punish you or ban you. They want to "reform you". Every person they send packing is less money. At the end of the day Riot is far from the worst. This is how virtually every publically traded company operates especially the billion dollar ones. Hard concept for a lot of people to understand. Companies are not your friend.