Can I ask a question...

So I go into a game, where our bruam is the nicest person in the world. Yay I love joyful supports, but there is one problem... He is duo'd with a majorly toxic yorick top laner. Who gave up at the 4 min mark when he gave fp to his laner and began saying things like "gg we lost , i have no jungle" "Our jungle is so Fking bad, he played malphite just so he could use the excuse he is a rock and cant move so he wouldn't have to gank because he doesn't know how".

Ok I can handle toxic people, but i am in just utter confusion of why people chose to duo with someone like this, someone who is very toxic and gave up very quickly (eventually he afk'd farm) , just why?...