Is this not a team game?

its a team game, but that doesnt mean your teammates have the same skill or intentions that you do. its also very hard to communicate with team-mates and team work is very rare. so unless your playing in a team with friends you have to play like its a 1v1. or else you will never move up in ranked.

It's basically 5 separate 1v1's, you just have to hope the people determined to be on "your team" don't lose theirs.