Why does bud walk from flint to grand rapids in the book Bud Not Buddy?

Bud walks from Flint to Grand Rapids in the book "Bud, Not Buddy" because he is determined to find and reunite with his missing father. He believes that Grand Rapids is where his father lives and decides to go there in search of him, despite the challenges and dangers he faces along the way. Bud's journey is driven by his hope and determination to find his family.