I suspect that it, like the "sinus" mentioned elsewhere, may well be a result of the scene (at least at the start) being dominated by people natively speaking Northern European Germanic languages.
I started learning English about 43 years ago, and I still struggle with when words are combined or separate in English because it largely follows no logic while in Norwegian it carries meaning.
writes "demoscene" all across the scene
^^^^^^^^^ ^^^^^^^^^
Which scene is that? Is it the scene about demos? A "demo" "scene" if you will?
"demoscene" comes from demo + scene. "demo scene" and "demoscene" refer to the same thing.
The latter is a more common spelling. We can also write "the scene" (meaning the demoscene) and "sceners" (meaning demosceners) and it's fully understood.
Alternative spellings of words don't have to be dominant or even popular, they just have to be understood. If you try and force someone to use a specific spelling even if you understood them with the spelling they used, that is somewhat jerk-like.
exactly what is stated. it is demoscene, and people been calling it such. https://www.pouet.net/ calls it demoscene, https://scene.org/ calls it demoscene, and so does https://assembly.org, which existed for at least as long as the demoscene been a thing.
so something that is called "demo scene" perhaps may designate other matter. the same way copyright is one word, and not "copy right", which is semantically diffrent thing.
it is not about what HN folk decides to call things, really. and written as "demo scene", well it took a second for my eyes to pattern-match the title.
English compound nouns can be open, hyphenated or closed. What is acceptable usage changes over time. Some say that compound nouns "harden", e.g "file name" became "file-name" became "filename", and they all mean the same thing, but currently "filename" is the most common spelling. "Foot ball" was acceptable in the 1800s but only "football" is acceptable now.
Your example, "copyright", has only existed in this closed form. "copy-right" and "copy right" are not recognised.
On the other hand, "demo scene" is a recognised variant of "demoscene". It may look as wrong to you as "color" looks to me, but it's recognised.
ORION, CODER:
-------------
LEFT THE DEMO SCENE FOR ABOUT A WEEK AS
HE STARTED CODING A GAME.
AFTER A WHILE HE CHANGED HIS MIND, DID A
DENTRO, AND RETURNED TO THE DEMO SCENE.
NOW A MEMBER OF FLASH PRODUCTION.
They also like to agglutinate words, e.g. copyparty, sizecoding and so on.
You can split or join the word if you like.