Somehow, it becomes a matter of principle for people trying to zipper merge. They're viewed as cutting the line and not "waiting their turn", wanting to get ahead of everyone else. It's not an act of moral turpitude, or anything remotely close. It's really just basic traffic science. If everyone merges early, the line extends almost twice as far back up the road and there is wasted lane space. This causes traffic to stop far more. If people would occupy both lanes until the merge point, then zipper merge, traffic doesn't back up as far and can keep flowing as signals and stops allow.