Because it doesn’t seem to matter currently if you play ranked games or casual games, the general experience tends to be the same. But one has numbers and things to go with it. You still get people playing to win in casual games and you get people dicking around having fun in ranked games, and the ranks don’t necessarily indicate how they play as a team and a whole bunch of other things that make it less than ideal.
Black Ops II had this in 2012. There were still ranked modes in the game, but you could select an option in the multiplayer and it would just auto-sort you into a lobby with an open spot in it. Every time the round would end, it would reset you into a new map and there would be new people there. I always found it way more populated than the ranked modes. You could always get a full lobby at 3 am.