I think when they were producing "THE JEM'HADAR", STAR TREK: GENERATIONS was being filmed and that bridge set was unavailable.
In universe, there's nothing to discount the possibility of a different bridge layout for the same class ship. Look at the Sutherland (TNG's "Redemption II") and the Prometheus (DS9's "SECOND SIGHT"), both Nebula class ships.
It could very well be, since both Galaxy and Nebula class ships use pretty much the same saucer design, that the bridge is a replaceable and interchangeable module. That would definitely explain why the bridge looks so different in GENERATIONS.
(Interestingly enough, it looks VERY similar to the layout in "Yesterday's Enterprise".)