And it's partly because Riot has trained people to think that the other report options don't carry any weight.
I think it's important to know that reports for griefing or AFKs carry just as much weight so that people can actually report for the right reasons.
For the people who downvoted, it's true.
I once was AFK for like 10 minutes because internet crash. I would totally understand if I was reported for AFK even though it wasn't intentional. But my team reported me for verbal abuse instead even though all I said was "im back, sorry. net disconnect".
Actually, Riot reviews logs, if you got punished for verbal abuse it was not because of false reports.
I think it's not so much that rito has trained people to think other report options don't work, but that verbal abuse/offensive language is the only one that generates immediate results (the automatic pop up).
They aren't reporting you because they want you banned. More likely than not, reporting you for afking or intentionally feeding won't actually get you punished because of the sheer number of offending games required to actually reach a punishment.
They're reporting you because they don't like you, and they're going to make you get the accusatory "you were bad last game" pop up from rito, and "hahaha, nothing you can do about it."
