Chat is easier to detect, which is why you get more chances to improve your behavior. People need to learn that it isn't a punish the worse offender type of system.
Gameplay is handled by another system. Yes, nearly everyone agrees this system needs improved. However, improving it isn't a simple task. Too often do people report others for gameplay offense where a gameplay offense wasn't committed, which in turn pollutes data that could be used to create a solid system. It would also be poor design to punish people simply for being bad.
Before someone decided to chime in with "Just bring back the Tribunal" two things to point out.
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Tribunal is slow, especially when you would want multiple players to weigh in for a judgement.
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Already mentioned that players don't have the best judgement/detection ability.