Question About Reports and Queue

I finished a game with a toxic Graves. He felt discouraged throughout our game. I kept telling him to hang in there. I didn't feel the need to mute him (thus he wasn't on my ignore list). Well at the post-game chat, he kept continuing his toxicity. I reported him, but neglected to place him on the ignore list. I queue up a few minutes later for another game. Sure enough, the person I reported is in my game, on my team again. I want to give him another chance, and I'm approaching this game with a clear mindset, but still it's kinda irksome that you can be queued with the same person you reported. It seems counterproductive if you're ditz like me and forget to place some on your ban list. Is there a reason why this happens?