I'd think, basically, if we could move the oceans and continents around so we had equal "weight" distribution across the "surface" of the Earth, there wouldn't be much wobble to speak with....much like balancing a tire. As is, there is unequal densities spread across the "upper crust" of the Earth, and thus we are slightly out of balance, and tend to wobble a bit.
A pretty simplistic view, but none the less......
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