The better wigglegrams were taken at basically the same moment and with cameras set a static distance apart along a single (usually) horizontal line. Those flow a lot more cleanly than the accidental ones where the camera moved an inconsistent amount and not along a single line so they're a lot jumpier and it interrupts the parallax effect that makes wigglegrams work.

I also noticed on the wikipedia gallery theres an example that repeats frames for smoothness! 1-2-3-4-3-2 makes it naturally smooth if you have more than two frames.

Yes, the author notes as much: ‘many of them come out as less "stereoscopic" and more "kinescopic" - like little unintentional movies.’