Wow, are you for real?!
When someone is on your tail! You may wanna see how close they are and which way they are veering before you pull a sick defensive maneuver.
I know how close an enemy is because the targeting area tells me to nearest meter. And when the enemy is behind me, the target hologram already shows me which way the ship is veering, not that it matters because I'm too focused on evading or repositioning my ship behind the enemy ship. Somehow this is enough because I've only lost one engagement against an elite NPC. A rear-view mirror makes sense in a car because a car operates in extremely close quarters and doesn't have shields. No need to fantasize about rear view mirrors and fuzzy dice. You're flying a ship in the vastness of space not driving a car to the drive-in theatre.