Photo © Nick de Jonge Photography
All this comes down to cost. Obviously, an over-wing airbridge would cost far more initial outlay but afterwards, are running costs (maintenance etc), similar? I'm going to go off in my fantasy world here but, *if* such gates were commonplace and *if* we get another long narrowbody design in the future, how much fuel will airlines save? The 757-300 is a good 30 tons lighter than the A300, which was built for similar missions.
Of course in a free-market world of privately run airports, the airport company would see no reason to build more expensive gates at the expense of MTOW-based landing fees...but it's great to imagine!