Here's why:
* Informal and affectionate: "Gattu" sounds like a playful and informal name, often used for children.
* Similar to other nicknames: It's similar to other common Hindi nicknames like "Chotu," "Motu," or "Munna," which are often used to refer to young boys.
If you're trying to understand a specific context where "Gattu" is used, please provide more details about the situation.