Knowing that it was a speed runner, it makes sense why he'd sell it. To be even halfway decent at speed running means he can make the game sit up, roll over, and play dead. He don't need no stinkin' ...
Editor's take: Though the troll enraged fans, this incident made for an epic speedrunning moment. The Zod rune represents countless hours of grinding, and Kano casually vendored it without a thought.