Quoted from SkyKing2301:Keep in mind -- the right slingshot is positioned just slightly more over the flipper than it is on the left side (due to the geometry of having a second inlane on the right side) ... so this means post passing left-to-right is normal, but right-to-left is more challenging.
I think it was an intentional choice in rush though I'm not certain why -- maybe for backhandable spinner? As far as I'm aware, Stern's other games (even Borg's other designs) with the same inlane configuration have symmetrical flippers and sling setups and can be post-passed either side -- e.g. ghostbusters, guardians, metallica, tmnt, tron