Here's why:
* Conciseness: "Rien" is simply shorter and quicker to say.
* Emphasis: The shortened form can sometimes sound more natural and conversational.
* Common usage: It's very common in French to drop prepositions like "de" in everyday speech, particularly in informal contexts.
However, it's important to note that:
* Formal settings: In formal situations, it's generally more appropriate to use the full "de rien".
* Context matters: While "rien" is accepted in informal conversation, it might not be suitable in all contexts.
So, while "rien" is a perfectly acceptable shortening of "de rien" in many situations, it's always good to consider the context and level of formality.