Why is Lightlark so popular (and how did it get a movie deal before publication)?

Lightlark, a YA fantasy novel written by Alex Aster was a BookTok phenomenon and remained on the NYT bestseller list for over a year. Universal bought the movie rights to Lightlark before the book was even released. Aster is in her 20s and it’s still very early in her writing career to see skyrocketing success. This sounds like every author’s dream come true, so how did it happen?