Personally, I think it's because I was looking for something more meaningful and genuine than what he was offering. But I imagine we'd disagree about that.
I actually feel kind of bad about this. While I do agree with this sentiment to a degree, I was going for snark instead of giving you a real, full answer. So, let me elaborate on my opinion in a way that isn't quite so pointlessly sassy:
I think that Zack Snyder is a filmmaker who relies very heavily on cliches and sentimentality. And when I say sentimentality, what I am specifically referring to is the use of images or concepts that elicit immediate emotional reactions or are tied in out social consciousness to things which are important to us, but don't actually hold much meaning themselves. A common example of sentimentality used in fiction would be:
You want the audience to be happy. So, the main character discovers a box of puppies on her way home from work. The audience is now happy. The story continues on.
OR
You want the audience to hate the villain. You have the villain drown a box of puppies. The audience hates the villain. The story continues on.
Most people like puppies and think they are cute, and so including them in the story makes that connection for the audience. But, in neither of those instances are the puppies woven into the narrative. The puppies aren't made to represent anything meaningful to the main character's backstory or the themes of the narrative when the main character discovers them, and the villain isn't built up beforehand as someone who would do this, and this act doesn't factor into his motivations, his actions for the rest of the story, or his personality beyond the rather banal detail that he's someone who has no problem drowning puppies. In neither case are the puppies and their discover/death integrated into the narrative for any reason other than to be cute. That is sentimentality.
Now, I don't think Snyder is as saccharine as the above example, but he is always using emotional shortcuts like that instead of taking the time in his films to set up and pay off important concepts and giving the audience the opportunity to come to care about them organically. The destruction in Man of Steel is a big example of this. We barely spend any time in Smallville and we don't get to know any of its residents other than the Kents before the Kryptonians start tearing up main street. We spend even less time with Metropilis before the battle there, we known absolutely nothing about that city even thought it is the thing at stake in the third act. We see dozens of buildings get destroyed, but we never see the actual effect that any of it has on human lives. We never see civilian reaction during the battle, and when we come back to Metropolis after the battle is over, everything is cleaned up like it never happened. Snyder is showing us things that are universally agreed upon to be sad or scary, but he doesn't actually show us the sadness or fear that should come with them. He is making these communities the thing at stake in these sequences, but he's not giving us any identity or familiarity to latch onto, we just have generic small town and generic big city. It is inherently hollow.
Compare it to Batman begins. That film spends an enormous amount of time establishing Gotham, both through dialogue and through cinematography and set design. By the time the third act roles around, we know Gotham. It has an atmosphere that we can taste, and a culture that we've come to understand, if only a little bit. So, when water manes start exploding all over the city, we have a better feeling for what is at stake, and during that action sequence we do cut away from Batman every once in a while to see what the citizens of Gotham are experiencing in all of that chaos through Rachel's eyes. The Dark Knight does an even better job, building off of what was done in the first film by using the architecture and aesthetic of Chicago to give Gotham a real sense of character, and spending a lot of time with the civilians caught up in The Joker's schemes. The difference is enormous.
And the thing is, there are people who don't care about any of this. There are people who respond to Snyder's emotional shortcuts exactly the way he wants them to. They get scared and sad because a building crumbling to he ground is a scary and sad thing. They don't need anything else to feel that. And that's fine. There's nothing wrong with that. However, the more detail oriented and subtler approach to achieving the same effect that I'm advocating for would not detract from their enjoyment. The people who only need to see the building fall down would not feel the feels any less if the film included all of those other elements for support that people like me want. The film would be just as effective for the people who already like it, and more effective for the people who don't.
And that, I believe, makes for better filmmaking.