Here's why:
* He was invited: Ron invited Harry to spend Christmas with his family.
* He had no other place to go: Harry had no family to go to, and Hogwarts was closed for the holidays.
* He wanted to experience a normal Christmas: Harry had never experienced a Christmas with a loving family before.
It's important to remember that the Christmas break in the first book is a significant plot point. It's during this time that:
* Harry learns about his parents' past: He discovers his parents were Gryffindors and learns more about their tragic fate.
* The Sorcerer's Stone is threatened: He learns from Ron's brother, Percy, about the stone and its potential danger.
* He starts to bond with the Weasleys: Harry begins to feel like he belongs in a loving family, which is a stark contrast to his miserable life with the Dursleys.
So, while Harry didn't stay at Hogwarts, his Christmas break was crucial for his personal development and for furthering the plot of the first book.