You wanna know why trolls exist?

Because people get fed up. At some point they just stop caring about the game or the teammates. If you subconsciously know your teammates are hostile towards you - even if they seem friendly at first, they're just constantly looking for any excuse to berate you, insult you, make you feel bad - then why would you care about them? Why would you want to help them win? So you just play for yourself. But at some point some people might get the idea that their teammates are their worst enemy. And in many scenarios that's the case. So what they do is attempt to make the "enemy" lose. Have you noticed that it's flamers mostly that complain about trolls in their games? "OMG Rito banned me for using chat, but they never ban trolls that ruin all my games". How many times have we read this? If you encounter trolls in most of your games you should strongly consider that it's you who might be the problem. I'm not saying I condone that, but it is entirely understandable.