Did you notice how Wilbur is always getting kept in a cardboard box, or put in his pigpen, or locked up in a crate? Most of the time, Wilbur doesn't get to roam free. Instead, his owners have figured out precisely where they want their little piggy to stay.
Sure, you could say he's trapped in these spaces. But you could probably also say that he's happy to be stuck inside them.
Let's investigate further. Take a look at Chapter Three, when Wilbur makes a break for it. He busts out of his yard, pushes open the fence, and ends up in the vast land of the farm. So what happens when the little piggy cries wee wee wee all the way to freedom?
Well, not much at first. Actually, Wilbur isn't even sure he likes freedom: "'I like it,' said Wilbur. 'That is, I guess I like it'" (3.17). Turns out freedom might be a bit of a letdown. (No one's bringing you daily slops out in the forest.)
But then Wilbur starts to get into his newfound liberty. He does a little jig and goes digging around an apple tree. Maybe freedom is actually pretty great. Of course, Wilbur also does lots of dancing when he's in his pigpen, so he doesn't really need to be outside to get his groove on.
So what do you think: do the fences represent traps? Or is life pretty good inside the gate?