I wrote and published a book, it is free. I make graphic mods, they are free. I created some 3d stuff, they are also free. I drew memes and guess what? I give everything away for people and get no a single cent for this.
That's great, and precisely what Creative Commons or Public Domain are for.
I release some of my work under those licenses too -- work for which I don't want limitations for what people can do with it or how they redistribute it. Creative Commons is actually a form of Copyright with a few less protections to the author.
I use plain old Copyright for some of my other work (like photographs which I happen to print, frame, and sell) precisely so that I can freely share it online and be protected from certain forms of redistribution. If I wanted to hide it in a box I wouldn't have created it in the first place.
Same concept applies to Space Engine! It is Copyright, and it is also free. You must not misunderstand what Copyright
means, or why people use it.
If you would have everything on the internet automatically be free from all protections whatsoever, I think you'd discover the internet a more barren place. I would have to find a different venue with which to follow some of my favorite professional photographers and musicians, for instance.