[crimony]

I suspect it because with a single piece axle the torsion forces trying to twist the wheels into negative camber are taken by the axle and the forces on the two wheels negate each other, leaving the frame to only have to deal with vertical linear force.

[rtkwe]

Maybe. You can get the same effect by putting two bearing on the inside of the wheel with a disconnected axel I think. A simple axel might come out cheaper than that though.