Here's why:
* "Statue" already implies smallness: The word itself suggests something smaller than a full-size human.
* Lack of a common diminutive: English doesn't have a natural tendency to create diminutives for nouns ending in "-ue".
Alternatives:
* "Statuette" is a common word for a small statue, particularly one that is ornamental.
* "Figurines" are also small statues, often made of porcelain or other materials.
* "Miniature" or "small" can be used to describe a statue that is smaller than average.
So, while there isn't a specific diminutive for "statue," you have several options to convey the idea of a small statue.