I like it that way and remember you can cut only part of it.  Sometimes, when I make games, I use the same big image couple of times because I only put part of it each time. Besides, in some top-down space game you can use 3000x3000 image as a paralaxed background, don't you think?

Best regards and thank you for your input :)

Well, I guess you didn't made many games in your life if you say so :) Anyway: there is a simple solution for your problem: just don't use them if you don't like them. 

I allready gave you an examples, but since you need some more ideas (it's a little lazy of you, don't you think?), here you go:

1. You can cut only part of it into the resolution you need or cut some part and resize it into resolution you need.

2. You can use it as a part of other background

3. You can use it as a part of sprite (example: the picture on the screen or in the picture frame)

4. You can use square background as a scrolling background in paralax, where in (for example) TD space game, the square background is drawed with some scrolling (I allready gave you that example earlier)

5. You can use it as an inspiration - after all they are CC0

Plase, don't be lazy and think about it yourself.

1. You ask me questions and I'm asnwering. 

2. I like making those backgrounds in the way I would use them in my games (and some of them were actualy made for games that I planned to do and didn't).

I know how it works and I'm aware that you need couple of layers to have the "real" paralax - but I didn't know better word (english is not my language) and actually you still can use those backgrounds in paralax, if you for example:

1. Add your own layers (like closer nebulas or something - Btw, tell me dude: you wrote you can generate your own backgrounds and it would be faster then just cutting/croping those (like those backgrounds are only for you) - why are you wasting your time on comments, then? :) )

2. Use couple of those with different blending.

Like I said man: just don't use them if you don't like them or upload your own with licence CC0 (since it's faster and easier :D )  and I will gladly download them (I collect CC0 graphics if they can be use to me) and you can be sure you will not have any whining from me, I promise :)

Now I think you don't know what paralax is :) But never mind, let's do it like this:

You are right, and those backgrounds should match only your projects :) But, no, those are not only for you :)

BTW: Thanks for inspiration, because I just had an idea: I will add (to this art post) the same backgrounds but tiled :D Maybe in an hour because I'm working right now.