Presumably the female reporter was assigned because she was the best fit for the story. Adding another colleague increases costs for the paper - & who gets the byline? The campaign assigning an intern also takes them away from other duties.The paper chose not to reassign a male reporter, or add another colleague as requested, and instead chose to report on what they see as an improper campaign request. In turn, the campaign could have assigned an intern to hang out with them all day as well, if they wanted the coverage.
Also while my position wouldn't change if the genders were reversed I suspect that a) the paper would be more willing to accede to the politicians request & b) it would be more damaging to the politicians career.