Here's why:
* Compound words are formed by combining two or more words. They can be written as one word (e.g., "fireplace"), hyphenated (e.g., "well-being"), or written separately (e.g., "high school").
* Prairie town is a phrase, consisting of two separate words that describe a town located on a prairie.
While it might sound like a single concept, it's not grammatically considered a compound word.