I may be off base, but don't confuse wiggling with just the car kinda shifting a bit side to side....
My terms may be off, but wiggling to me is when the wheels are actually sliding or moving back and forth on the track which definitely cuts down on speed....
but if you look closely, there are cars where the rear of the car seems to kinda shift side to side just a small bit...but the wheels themselves are not sliding or moving side to side....maybe this is just a function of the bore to axel diameter difference so the wheel itself is staying on path and not sliding but is sort of just tilting or oscillating a bit.....I think this could also cause some slow down depending on how much there is or how severe it is....but perhaps not as much as outright wiggling....
as such maybe that's why some cars that do show this oscillating movement still put up fast times versus cars where the wheels outright slide or or move off line...
Just my own thoughts....