You try making hundreds of buildings with all the nessesary details, and then a complex and detailed road system that runs throughout all of this. Then add cars, pedestrians, seagulls, airplanes, helicopters, and sky effects. Then find a way to get the playstation 2 to run all of this with no slowdown in the middle of a heated gang war.

Vs running some copy-and-pasted cel chaded water for a certain distance on the (slightly) faster gamecube. Even halflife can do that.