Why Do People Troll In Ranked?

In all my accounts that ive played rank in, everyone on my team trolls except for mid and top usually (I play Fill, usually get support everytime though). They troll either by playing an area they dont have much experience in, "Hey guys, I want to learn Jungler this game". Why dont you go to nonranked for that? Or people will choose their lanes champ, but its literally the weakest champ for that position unless youve mastered that champ. Last game I had an Ashe as my ADC, out of my hundreds of games ive played against and with an Ashe, ive only had one good one. Or my support will be Heim, I dont recall Heim being a support, id put him under the Lane Bully class.

So my question is, is why do people go to rank, try something new that theyve never done before instead of just going to nonranked or custom games to try it? As a filler, this makes me annoyed because I can do just about every lane (Mid lane i struggle with but its rare for me to get 3 deaths as a mid laner at the end of the game), and if they cant do their lane correctly, why should i even fill?