Complex sentence: Many of them also work as "script doctors", attempting to change scripts to suit directors or studios; for instance, studio management may have a complaint that the motivations of the characters are unclear or that the dialogue is weak.
Split into simpler sentences: Many of them also work as "script doctors", attempting to better a script to suit the desires of a director or studio. For instance, studio management may have a complaint that the motivations of the characters are unclear or that the dialogue is weak.