[To be clear, the below is me agreeing with you]

Norwegian is almost as compound-happy as German, and we could've filled many volumes with compounds. But what generally happens for one of the compunds to enter the dictionary is that the compound needs to have a meaning that is non-obvious from the individual parts, at least to some people, and typically that the compound has a non-obvious meaning if interpreted as two separate words.

E.g. "akterutseilt" is an example. "Akterut" means behind, aft. "Seilt" means sailed. "Behind sailed" helps as a way to remember it, but it's not obvious whether it's strictly a sailing term, or means that you've been left behind or have left someone else behind.

In this case if you say someone has been akterutseilt, it means they've been metaphorically left behind, often by their own failure to keep up.

Those kinds of compounds deserve dictionary entries whether they are actually written in two words or one, because they function as a single unit however it is written.

I think black hole is a perfect example in English. And in fact, this is a compound that is written in two words in Norwegian as well, but is in Norwegian dictionaries despite that[1] as "svart hull".

[1] https://ordbokene.no/bm/svart%20hull

And I attempted to add your 'svart hull' note.

Fun fact: I looked this up in the online version of the Duden (the predominant German dictionary). It does have an entry "Black Hole" (so the English term!) but not for "schwarzes Loch", which is the normal German term for it.

(In the printed versions, you might need to go to the Universalwörterbuch or so to find the English entry, it might not be in the normal "Die deutsche Rechtschreibung"; I have not checked.)

Great example — I added svart hull to the article as an illustration of a language that writes it as two words but still puts it in the dictionary because the meaning isn't obvious from the parts. That's exactly the instinct English lacks.