Complex sentence: Mayer's choice seemed unusual, because up to that time Stewart had written only light romantic comedies featuring wealthy East Coast socialites, but Mayer felt Stewart's strongly leftist political leanings would enable him to turn out a better screenplay.
Split into simpler sentences: Mayer's choice seemed unusual, because up to that time Stewart had written only light romantic comedies featuring wealthy East Coast socialites. But Mayer felt Stewart's strongly leftist political leanings would enable him to turn out a better screenplay.