Spent a lot of time braining this and sketching in mspaint and this is the theory I came up with. Not sure if it's correct and I'm very noob at physics so duno how well I can explain. Also I'm very tired so not sure how much sense this will make.
I think there are two different effects causing pops. Which one has the most effect depends on moment of the bike and angle to the ground.
Full Bike effect: Rotation of the wheel is transfered into rotation of the whole bike. This is easy to see if you are free-falling and try to accelerate and brake.
Wheel effect: Rotation of the wheel stops.
These example images are from warm-up and the famous wheelpop by bene
. What actually happens if the wheel lands at the left side of the hill, is that the wheel pops the other way. Rec: http://www.recsource.tv/r/jiymxpvgwo
img01: Wheel is rotating clockwise.
img02: Braking causes the wheel to stop rotating, and all the energy is transfered in a single frame(?). When you stop rotating clockwise, that means the wheel is going to rotate the opposite direction (anti-clockwise) for one frame.
img03: Braking will also cause the whole bike to rotate anti-clockwise.
In the case of landing on the right side of the edge:
The whole bike 'wants' to transfer the rotational energy to the bike, but instead it is transfered as grip directly to the wheel. I imagine it kinda like the backwheel wanting to go up in the air, but instead the grip of the wheel is holding it down. The wheel trying to 'lift-off' the ground trumps the other effect.
In the case of landing on the left side of the edge:
Notice that we are alovolting here, so the wheel and bike is already being pressed towards the ground. The anti-clockwise effect on the whole bike does not have an effect on the wheelpop because it can't make the wheel leave the ground at this angle. This is probably the deciding factor of which direction the pop will go, whether the rotational effect (the effect which makes the backwheel drop), can make the wheel go off the ground or not.
If I try to visualize both scenarios I'm thinking something like this:
It's probably more complicated than this, and yeah I don't know physics very well so my terms are quite random, maybe I'm partly right and maybe I'm totally off, no idea.
Also here is kinda related video from smarter every day https://www.youtube.com/watch?v=zJX_Oh4yVnc
Here is one recent new rec not mentioned yet I think, double pop rec: http://www.recsource.tv/r/zurkecwjad
If anything scientific it probably proves that throttle is not what makes it pop (as you can't throttle both ways), but this is easily testable without double popping so it's probably just a fun/cool trick.