Why doesn't Jhins Bouncing Grenade proc his passive on his W?

So I've been playing Jhin since his release and personally he is my favorite ranged ADC. However I've run into plenty of situations where I'm reloading get caught and die which albeit that's his main counterplay there were plenty of times where just throwing a grenade and landing my W would've got some distance between me and my foe and likely would've saved my life. So what are your thoughts?