I'm not sure it's fair to put all that blame on Snyder though. You gotta think that a lot of the action was written into the script with Snyder just following that. Now this is merely an assumption on my part, it could very well be Snyder's doing...
You're right, it was in the script. Goyer confirmed it in this interview he did right here.
Makes little difference. In Hollywood feature films, screenwriters have no power; they're seen as hired contractors whose job is to write what the director and producer tell them to write. The specific words and connective tissue come from the writers, but the decisions about the key story points, about what goes in the film and what doesn't, come from the director and producer.
That's why Goyer's record as a screenwriter is so inconsistent, why -- as JacksonArcher
said -- the quality of his work depends on the quality of the director overseeing it. It's because the director is the one making the real decisions.