[Matt]

I wonder why so many ppl use the elbow plane on the downswing...

Is it because that's what they do naturally or that's what's taught/a result of what's taught?

They've just been told for so long that they had to shift back down. What mainstream instructor is teaching a zero shift on the turned shoulder plane? None. Every month in the magazines you read about how you get to a steeper plane going back and have to "drop it in the slot" or some nonsense on the way down. While that's certainly a viable option, it's not the only option nor the most efficient.

The sweetspot certainly doesn't want to fall back down. It just wants to take a straight line to the ball, following PP3.