I didn’t mean to take this thread off topic.
To the OP’s question: I think a lot of priests just don’t want a lot of nasty letters to the bishop over something they’d consider trivial. I’d bet that many priests are not in a position to explain the rationale for ad orientem and, as such, don’t feel that it is something that could be successful. To make that type of change, you have to catechize the people well and prepare them for it.
On the flip side, those priests that see the value of this liturgical posture and really want to [re-]introduce it, they study up on it and gradually bring it to the people (example: holy days or special occasions, then work up to an early Sunday Mass, then finally make it a standard practice). This tends to be more warmly-received.
However, you will always have those in a parish (usually the Old Guard who have been there forever and consider the priest a visitor) who will stir up a rebellion regardless of how the majority of parishioners feel, and those few letters to the bishop will elicit a phone call to the parish priest. If the priest is prepared for this, it is usually not a big deal, but if he is not, then it is a hill he’d rather not die on.