Because we still did not prove that there was something else out there. This is what I think. There is. Because that we have a milky way that has a lot more galaxys than us. I am guessing that there is a another galaxy like us a human on a another world. We couold meet them and talk to them and do fun things. That is why, I guess there is.
Here is the Andromeda Galaxy, for instance: https://en.wikipedia.org/wiki/Andromeda_Galaxy
Here is the Triangulum Galaxy: https://en.wikipedia.org/wiki/Triangulum_Galaxy
Here is the Large Magellanic Cloud:
All of these are nearby galaxies, belonging to the so-called Local Group, which consists of galaxies that are gravitationally bound together. Our galaxy, the Milky Way, also belongs in this group.