There's no doubt in my mind that lag is the cause of rage quitting.
But how often do players rage quit when games aren't going their way? I find it selfish that players are happy to stay in when they do well but once they do bad, they leave not even half way through a match in progress.
I thought that it was my scorestreaks that made players quit but once I switched to team support scorestreaks (no Lodestar, no Swarm, no Dogs etc), people still left.
YouTubers are hypocritical when it comes to rage quitting. Whilst they complain about people leaving their "YouTube worthy" matches, they leave when their match isn't considered "YouTube worthy" to watch.
It's gone to the point where most COD players believe that everyone's a winner.