In English "car factory" are two words. In Dutch an "autofabriek" is one word.
A dictionary might choose to list the most common compound words which quickly adds up.
For instance, "autógyár" (car factory) is a compound word made up of "autó" (car) and "gyár" (factory).
I suspect the reasoning is the same for Dutch.
Example in Dutch: you can say "losgeld" (literally: loosemoney, money that loosens/releases something; specifically: ransom) but you can also say "los geld" (loose money) which is like spare coins you have in your pocket or so.
In 2020, a supermarket requested that people don't pay with losgeld but by card instead, so they meant to say "please don't pay with cash" but they said "please don't pay with ransom"
What's more, English also does togetherwriting. Are "web site" and "website" counted as two words when doing an English word count? Or are words like "web site" simply not included (only "web" and "site" separately)?
(Fun fact: website is webseite in German, where "seite" actually means "page" and not site at all, so you're really saying webpage which, in turn, happens to also exist with a nearly interchangeable meaning in english. I wonder how many circles of meaning there are like that! ChatGPT wasn't able to come up with any, at least not without prompt tweaking or follow-ups)
"As a member of the Germanic family of languages, English is unusual in that even simple compounds made since the 18th century tend to be written in separate parts. This would be an error in other Germanic languages such as [...] German, and Dutch. However, this is merely an orthographic convention."
And this also:
" In Dutch and the Scandinavian languages there is an unofficial trend toward splitting compound words, known in Norwegian as særskriving, in Swedish as särskrivning (literally "separate writing"), and in Dutch as Engelse ziekte (the "English disease"). Because the Dutch language and the Scandinavian languages rely heavily on the distinction between the compound word and the sequence of the separate words it consists of, this has serious implications. In Dutch, compounds written with spaces may also be confused, but can also be interpreted as a sequence of a noun and a genitive (which is unmarked in Dutch) in formal abbreviated writing. This may lead to, for example, commissie vergadering ("commission meeting") being read as "commission of the meeting" rather than "meeting of the commission" (normally spelled commissievergadering). "
I'm not sure Wikipedia is right here. It's not necessarily an error to write a space in between two words: it just changes the meaning, and it's an error if the meaning doesn't exist (just like in English: "ahorse" doesn't form a meaning like "alike" does, and so is likely a typo for "a horse"). It's also not "merely an orthographic convention" the way that, e.g., starting sentences with uppercase is a convention that could easily be changed because the sentence separator "." is already there.
The space separates two words. Having no space means it's one word. Adding the space means that what came before must be a different word, like an adjective or a preposition.
Take something like "patient data": is this data patiently waiting, or is it about data belonging to patients? In Dutch/German, "patientdaten" is unambiguously one thing and "patient daten" is unambiguously another (when pretending that "patient" exists as an adjective in Dutch/German, which it actually does not; but examples where it also exists as adjective are plentiful, see <https://news.ycombinator.com/item?id=40399141>).
