Welcome to the forum!
It's mathematics. There is a range of adjustment for each stabilizer- typically, holes line up (to pin the stabilizer) from 3/16" to 1/2", depending on the manufacturer. Implement frames can vary in width, so once the lift arms are attached to the implement, it's possible that the implement can be centered in reference to the tractor, or it can be to the left or right, if the width of the implement isn't divided evenly with the combined adjustment of the stabilizers.
I build telescoping stabilizers for a living, and this has been my recommendation to customers- it isn't operationally necessary for the implement to be perfectly centered, unless the tire implement isn't covering the track of the tire or if there is interference between the stabilizer and the tire. In most cases, it's OCD, not a physical problem.
I would suggest this procedure- there is a loose way to pin the stabilizers, and a snug way. If you install an implement and pin the stabilizers as it sits, there can still be an inch or more of side to side play. I recommend that you practice this- once the implement is installed, raise it up enough to move it side to side. Position the implement where you want it, and pin one side. Then, push the implement to one side or another (preference) until the pinned side is tightened up, and pin the other side. This will reduce the sway to the minimum amount.