Simply because the universe, to the best of our knowledge, has no center.

We cannot say for sure but if our physics is right, the universe is very likely unbound and infinite. There is no edge and no end.

Then there is the thing we call the observable universe. It is what it sounds like, the universe we can observe.

Because light takes time to reach us, we are looking back in time the further away we are looking in space.

We can look so far back, the universe was a opaque gas cloud everywhere, and very little light from that time escaped that gas. Eventually we hit a theoretical stop, the birth of the universe, and we cannot look further back than that.

Where that edge is lies our cosmic horizon.

So our observable universe has a size, and that is 13.8 billion light years (the age of the universe) + the expansion of space, so 46.5 billion light years in every direction from here.

Actually, not here, but from wherever you are observing.

You are in the most present you can be, which also means you are in the most center position you can observe the universe, which means you are always in the center of the observable universe.

You are literally the center of the universe and with science to back it up.

But unfortunately that is not so special, since that is true for everyone and every point that exists.

But for the whole infinite universe, if it is truly infinite, there is no center.