Zipper merge works great if everyone accepts the concept of late merging. But not only is that not the case, many early mergers are religiously fervent about everyone has to get over out of the lane that’s closing at the first sign, usually a mile or mile and a half away, because it’s only fair. My younger brother is that guy and he’s very adamant about it. Plus, every once in a while, you will see someone playing Corporal Lapdog, using their car to block the lane that’s closing so that no one can drive all the way to the end and late merge because, I guess, they think they’re helping maintain societal law and order or something.