First of all, they do ban INTENTIONAL FEEDERS. The problem is what you call "Intentional" and what they call it is different. To you, everytime somebody has a bad game and has a bad score. You want them banned. If somebody is just a bad player in your game. You'd want them banned. Intentionally feeding is more somebody running it down and feeding the enemy kills intentionally (In other words, that is their actual goal is to feed them kills to ruin the game) not somebody getting outplayed and dying.
For example I see a 1/8 draven game on your record. I'm sure if that was a teammate you would complain about them trolling and feeding. But riot also does a poor job in explaining what "Intentionally feeding" is. So people just parrot what streamers call "inting" and thinking it's the same thing that's reportable.