Here's why:
* It's a proper noun: "Social Studies" is a specific name for a field of study, just like "Math," "Science," or "English."
* It's often used as a title: When referring to the subject in a school curriculum or course, it's treated as a title and capitalized.
However, if you're using "social studies" in a general sense to describe a type of study, you wouldn't capitalize it.
For example:
* Capitalized: I'm taking Social Studies this semester.
* Not capitalized: My favorite part of school is learning about social studies.