@Riot why was the rune system created?

According to them (from what I heard), Masteries are the more situation-specific buffs, and they force you to invest in a specific tree if you want a certain bonus. Meanwhile, Runes are effectively masteries without said requirements; you don't need half a page of AD runes before you can get Crit runes, or something like that.

{quoted}

Serious question, I'm curious.

Gives you a reason to buy champions with money instead of IP... literally that is the reason

Good business model, promotes long-time playing and grinding + has made them alot of $$$