An alternative explanation is that this intentional imperfection exists to match the unavoidable imperfection which occurred when the cursor graphic was originally drawn as tiny low resolution 1-bit pixel art. It looks correct because we're used to it being slightly wrong. And when viewed at a normal size, the difference is barely perceptible anyway.
[0] https://mspoweruser.com/why-windows-10s-asymmetrical-cursor-...
[1] https://old.reddit.com/r/TIHI/comments/fwnep0/thanks_i_hate_...
[2] edited, thanks jusuhi