If they aren't setting the game during the events leading up to and during Robert's Rebellion, they're doing it wrong. That time period has a shit load of characters we care about and would be a great setting for a game.
Edit: I am hijacking my own post to feverishly gush over my own GoT vidja game pitch.
My pie-in-the-sky dream GoT game would be set before, during and after the rebellion taking place across the entire continent of Westeros sans perhaps north of the wall.
Imagine if the player character was a bastard born in one of the nine major regions (North, Vale, Iron Islands, Riverlands, Crownlands, Stormlands, Reach, Westerlands, Dorne), with the player choosing where they want their character to be from and which house they serve. They story at the beginning would differ depending on where you start from, but all 9 paths would mostly follow the same beats: the tourney at Harrenhal, battle of Ashford, The Trident, sack of King's Landing etc.
Your ultimate goal is to assist your liege lord in either defending the crown (Targaryen, Lannister, Tyrell, Martell), overthrowing the crown (Baratheon, Stark, Tully, Arryn) or take advantage of the chaos and reave where you please (Greyjoy).
Your skill tree could have 9 branches: Father, Mother, Maiden, Smith, Crone, Warrior, Stranger, The Old Gods and The Drowned God.
NPC's refer to you by your bastard surname (Snow, Stone, Pyke, Rivers, Waters, Storm, Flowers, Hill or Sand) for maximum immersion
Side quest potential is enormous here:
-Recruit/capture potential brothers for The Night's Watch
-take care of The Smiling Knight
-find all of the Weirwoods in Westeros to see visions of the past and future
-beat back Hill Tribesmen in The Vale
-investigate reports of a Faceless Man sighted in Westeros
-investigate an underground cult of religious fanatics called "Sparrows", join or destroy them
-fuck all the whores in Westeros and "make the 8"
-study at The Citadel in Oldtown like a nerd
-assist the head of customs in Gulltown with shady dealings (some dude named Petyr? Seems trustworthy)
-go to Gin Alley in King's Landing and give Karl Fookin' Tanner 6 silvers to kill a man
EZ DLC MONEY:
Greyjoy Rebellion DLC
"Beyond The Wall" expansion (Bronn mentioned he's been north of the wall before, get him in there)
Where's my check GRRM