Two words - situational awareness.
The G1000 combines nearly all the information you might want into a relatively intuitive package that is very easy to see.
Why do people buy a 50 inch tv in preference to a 30 inch tv or equivalent computer screens. Simple - display the same film or information on a larger screen and it is easier to take in the detail. Same with a G1000.
Then add in a host of possible features like overlaying instrument approaches and profiles, TAS, weather, etc and you have a powerful set of tools.
As IOs says field maintenance presents its own problems. Personally I think the user interface could be more intuitive - Avidyne 9 is a better example of how it should be done - but all in all it is the way ahead.