The biggest motivation is to increase viewership while supporting a certain candidate and promoting him. Privately owned media sources are usually biased towards someone and help them while they show bad things about other candidates. In return, they expect support from the candidate if they ever get into a position of power. By being controversial, they get new viewers and earn more money.
Private businesses are primarily motivated by profit, and a media company that is privately owned is no exception. This motivation might influence how a certain story gets covered or whether it gets covered at all.
In terms of political issues, a privately owned media source will probably cover only stories that will be likely to increase readership or viewership. Or the source might put a shocking spin on stories to increase interest.
