Same reason we have windows on airliners (with all the structural problems that causes) - humans.
The Space Shuttle didn't have monitors when it could have done, likely due to situational awareness - a flat 2D view on a monitor is always trumped by a 3D view out of the window - for situational awareness if nothing else (try flying an aircraft on instruments only and you'll get the idea, or a flat screen flight sim vs the Oculus Rift etc etc). So it's massively advantageous for the pilot.
Also humans like to see outside, which is why there are windows for passengers on airliners - there's no sound structural reason for them, but humans aren't overly keen on being strapped into an enclosed tube which they can't see out of while they rocket through the atmosphere via the safest form of transportation on the planet - go figure.
And lastly (as already said) - it's a game. If you make it 1000 years into the future, you can tell me that you told me so, but I have a feeling I'll be past caring....
Note that the original Elite it *was* a viewscreen - see the pic of the Cobra flight deck in the Space Traders Flight Training manual. (but we've come quite a way with computer graphics since then!)