Why does it keep putting me on the rookie team?

lmost every time I join a team in a deathmatch, it keeps putting me on the rookie team, and I end up having to leave. Every time I leave and join a new match, it puts me on the rookie team again, so I leave once more. At the beginning of the match, the enemy team captures all the zones, and there's no point in playing anymore. It takes me around 5 minutes to quit because it keeps assigning me to such a weak team. Is this happening because I keep leaving matches, or is there another reason? I sometimes have to leave and join different games 6 times in a row without even finishing a single match.