We are not told why Saul did not honour his commitment to David. Most likely the marriage to Adriel would have served to strengthen relationships with an important noble. It could also be that Saul wanted to slight David and remind him of his inferior place and position.
19 Lorsque arriva le temps où Mérab, fille de Saül, devait être donnée à David, elle fut donnée en mariage à Adriel, de Mehola.