Here's why:
* Compound words are formed by combining two or more words, either with or without a hyphen. For example, "sunrise" or "high-pitched".
* "Surroundings" is a single word with a meaning that is different from the individual parts of the word. It refers to the environment or things that are around something.
While "surround" is a separate word, it's not the case that "surroundings" is formed by combining "surround" with something else.