For instance a "blackboard" isn't a "black board": it is not simply any old board that is black. I.e. the semantics of the composition is not the composition of the semantics.
Some compound words in English have a history which starts as two separate words, then later joined with a hyphen, an finally conjoined without a hyphen. This roughly follows their evolution into a non-compositional noun.
"Newspaper" was once "news-paper" for instance.
Words like "high school" are the unfortunate exceptions; a high school isn't a school which is high, yet it's written as if it were two words. It's certainly not spoken that way; there is a difference between "high class", "high seas", "high concept" and "high school". The "school" is uttered without the slightest pause in front of it, and de-emphasized. Exactly like "board" in "blackboard", or "wife" in "housewife".
For what it's worth, at least English orthography doesn't string together long runs of words into an undelimited string.