Here's why:
* Chocolate is a food: Unlike animals or objects, food items generally don't have established collective nouns.
* Variety of forms: Chocolate comes in many forms (bars, chips, truffles, etc.), making a single collective noun difficult to apply.
However, you could be creative and use:
* A box of chocolates
* A collection of chocolates
* An assortment of chocolates
* A feast of chocolates
* A bounty of chocolates
The best choice depends on the context and the specific kind of chocolate you are talking about.