Some people don't have a mic. Maybe they had one, but it broke or got lost. There's also people in the world who don't speak english. Why don't they go to pubs then?
Maybe they don't want to play with people who don't even care about the objective. I don't know if Ranked Play on AW already got any official rules applied, but in Ghosts, I went solo in Clan Wars sometimes just because all killstreaks including guard dogs with the ability to teleport, ninja squad members, hinds getting you 10 kills while you sit in a corner etc. were banned. Same goes for IEDS, amplify campers and so on.