Seriously?
“Cheat”, as you say.
For it to work ideally (no one in either lane really brakes at all), you need to start lining up positions well before that.
When people are doing it right, there is no “steady stream,” in the sense of a series of cars end-to-end in one lane. And certainly no “forcing.” Every vehicle, by the time it reaches the merge point, is lined up with an open space in the other line. And the two just shwoop together.
The zipper merge I’m usually involved in is on a busy street which goes from three lanes to two. There is no empty space usually, so each car slows just a bit to let the appropriate car from the merging lane in. When a car on the left leaves too much space at the merge point things get confused.
You do kind of keep track of who will merge in before you (I like to be on the left here) but the situation at the merge point is what is important.