Why did Angela's Ashes win the Pulitzer Prize?

Frank McCourt's autobiography, Angela's Ashes: A Memoir, won the 1997 Pulitzer Prize in the "Biography or Autobiography" category because the Pulitzer jury thought his work was Excellent and the Pulitzer Board agreed. They did not release a public statement documenting the reason the book won the award.

An excerpt from the book's dust jacket may give a better explanation:

"Angela's Ashes, imbued on every page with Frank McCourt's astounding humor and compassion, is a glorious book that bears all the marks of a classic. As Mary Breasted, author of Why Should You Doubt Me Now, said: "Frank McCourt's book is deeply moving, for his searing story is true. No one has ever written about poverty or childhood like this. That Frank McCourt lives to tell the tale is amazing. That he could create out of such squalor and misery a flawless masterpiece is nothing short of miraculous."