While I don’t disagree this CAN be a riding/training/saddle fit issue, it is not guaranteed. Read my last post for an explanation of how it really can be a real physical issue.
Horses “cheat” by tilting their head either because it’s just plain ol’ easier, and that is a training/riding issue, or they cheat like that because it is very difficult, or impossible, for them to physically keep their head vertical and flex laterally at the poll. If the atlas is tipped, it can be very easy to flex laterally and remain vertical one way, but absolutely impossible to go the other way correctly.