If you look at the driving wheels of an old steam locomotive,
there is a connecting rod attached off-center to the wheel by a crank pin.
The pin and rod contribute weight that unbalances the wheel.
If you're going to add weight to correct the imbalance,
you don't want to add the weight in the same place as the pin.
You want to add it somewhere else.
So the new weight is somewhere "away" from the old weight.
Here is an example (source: Wikipedia, photo by Sean Lamb).
The crank pin and connecting rod are attached on the right side of the wheel in this photograph, so the counterweight has been added to the left side, about as far from the pin as possible.
Note that there are many meanings of the noun offset
(as shown in the Merriam-Webster definition, for example).
Few of them involve counterbalancing, and (as far as I can tell)
none implies a long distance; even in the archaic sense of the act of setting off on a journey, the offset of a trans-oceanic voyage is completed once you have left the dock.