Video games are just that. Games. Do you watch football games for the religious experience? Apples and oranges.
As for morality, Christianity has no monopoly on morality. I would imagine being preached at while trying to solve puzzles or nuke super mutants would be a crippling experience. If there were a market for religious video games, be sure there be plenty for the buying.
I could easily image a gory Crusader war game, or chaplains in U.S. military war games.
How about Just War in combat games.
All possible. As I said, fiction was rife with Christian morality and themes before 1900.
Treasure Island is a great adventure novel, chock full of Christian morality.
As for football, look at how Tim Tebow has been persecuted for showing a tiny amount of Christianity in football.
The exclusion of Christian morality has been deliberate.
It is not because it is unpopular. It is to make it unpopular and un-cool...