Why do fictional space battles look two-dimensional?

Why do space battles so often appear linear even though space is three-dimensional?

They are staged for two-dimensional human viewing, although genuinely three-dimensional combat would demand all-around maneuver and weapon coverage.

Many flat space battles come from staging stories for human viewers on two-dimensional screens. Games such as Battlestar Galactica: Deadlock handle three-dimensional maneuver more convincingly. Even there, some ship weapon layouts leave guns able to cover only narrow upper-forward or lower-aft arcs. A spacecraft needs sensors and weapons distributed for threats arriving from every direction instead of reproducing a surface fleet on an invisible ocean.