Why are most Trolls ADCs?

I understand the whole Tyler1 fanboy thing but most my games preseason have had a ADC that starts to troll as they care too much about their KDA over objectives. My last game I had a Lucian by the name of "LuKeered" who was 1/4/0 before going AFK and then running it down top and mid feeding a Sol and Darius. He went AFK after I ganked bot lane and got a double kill which was also followed by me and the sona taking first tower. This affected my game more as I had to hold bot lane meaning I couldn't gank other lanes leading them to advance due to his childish behavior. It just seems to be ADC that troll in most games I play and watch as they care too much about their KDA. I have nothing against ADC's as I play there quite a bit, its just I'm getting tilted as I want to get a late push to Gold before the ranks restart but these trolling players makes it harder and nothing seems to be getting done about the players that are reported as I like to check their profiles to see if they have been banned and 9 times out of 10 times they haven't and they do the same in other games. Rant over
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