Here's why:
* It's unique: Anthologies are collections of *works*, specifically written works like poems, stories, essays, or plays. It's not a group of living beings like a "flock" of birds or a "herd" of cows.
* Specificity: The word "anthology" itself implies a collection of specific things (written works). We don't use it to describe a collection of random items.
Instead of categorizing it with other collective nouns, it's better to understand its specific function.
Here's how you might describe it:
* A collection of literary works: This is the most accurate and general description.
* A compilation: This emphasizes the act of gathering and putting together the works.
* A compendium: This implies a comprehensive and organized collection of works on a particular theme or subject.
While there are other words for collections (like "album" or "portfolio"), "anthology" has a distinct meaning related to literature and is not typically grouped with other general collective nouns.