We humans do that because we cannot imagine something out of our world. why aliens on sci-fi movies always reminds of mixed by crawlers, reptiles and sea creatures as well as humans. Yet, there are some that can invent new stuff that is not connected to something else. The radio is an example of that. same goes for the satelites and the light bulb. I am sure there is more great inventors out there that can imagine something out of our world. Sadly, I am not one of them. My inventions can always be related to other stuff we already know of.