I think what your missing here is the meaning of sci-fi

A literary or cinematic genre in which fantasy, typically based on speculative scientific discoveries or developments, environmental changes, space travel, or life on other planets, forms part of the plot or background.

They are based on speculation and/or fantasy. Not facts. They are fantasy to make an interesting world. It is only to make ppl enjoy their time. Not to be something true. While it is entertaining i hope you realise that what you see isnt true and is most of the time based on speculation and not facts.