Here's why:

* The universe doesn't have a center. Our understanding of the universe is that it's expanding in all directions, with no single point being more central than any other.

* The Big Bang wasn't an explosion in space. It was an expansion of space itself. The universe was incredibly dense and hot at the beginning, and it has been expanding ever since.

So, while we can talk about the center of the observable universe (the portion we can currently see), there's no central point to the entire universe.