It can be though. Ever head of Tabletop Simulator (which is literally what it says it is)? Or Ticket to Ride (a boardgame turned into a video game)? Even the classic cRPGs are pretty much emulators of PnP RPGs. Maybe not in the sense of amount of interaction possible, but certainly in how they incorporate all of the rules within a video game.A video game is not PNP.
But I do agree with you that a video game doesn't have to be an exact reflection of PnP and its rule set.