I think that last paragraph has a clue as to the problem and solution. Those questions all are assuming someone other than the devs are responsible for deciding

I think that last paragraph has a clue as to the problem and solution. Those questions all are assuming someone other than the devs are responsible for deciding things. If the devs are making those calls, they won't wonder why things are taking so long or what could have been simple. PMs should help act as an intermediary with the customer and convey that domain information to the devs but shouldn't have any real say over the roadmap or features as they don't have the knowledge or experience to make those calls.