Why did David Yates choose Emma Watson to play the part of Hermione Granger?

David Yates did not choose Emma Watson to play Hermione Granger. Chris Columbus, the director of the first two Harry Potter films, cast Watson in the role.

Yates joined the franchise with "Harry Potter and the Order of the Phoenix" (2007), which was the fifth film in the series. By this point, Watson was already established as Hermione.

While Yates did direct the final four Harry Potter films, his involvement came after Watson was already cast. He simply continued with the casting choices that had been made previously.