When you enter a job role, Workfront will populate people that have that primary job role. Our Marketing team wears many hats, but WF will only populate their primary role, so if they enter "Web Admin", only people with that as their primary will show in the suggestions. There should be a way for any role assigned to a user would populate that users name when the job role is assigned to a task.
Ex - Andrea's main job role is as the Assistant Marketing Director. She will be the designer of an ad that will go out in a few weeks, but if she selects "Design" as the job role, her name does not populate because it is listed under her "other roles", not her "primary role".