I think a lot of the lack of motherhood in games is related to endless reasons why female characters are kept young, single, slim and sexy (whether it's through magic, time travel, frozen members of ancient races etc) whereas male characters can be happily stomping around in middle-age, even deadlier bad asses than they were 20 years previously. For some reason game designers don't like to imply that a female leading character has had/is having a meaningful relationship with any npc, so they can be a kind of idealised proto-girlfriend for the player, whereas it's ok for a male character to have had plenty of relationships.
Perhaps there's still an element of assuming the audience is male, so the thought process is that a male leading character's child will tug on the player's heartstrings as they play that character's father, but a female leading character's child is the child of another npc male character who has had a sexual relationship with the lead character, and so is presumed to be less appealing to a young male player.
Before we look at the lack of mothers, I think we'd also need to look at the lack of leading female characters of an age where that could be likely. We need more variety in protagonists in games (something more likely to happen with more diversity in the people making them), but at least going from few female protagonists 20 years ago to lots of pretty young female protagonists today is progress. Maybe one day we'll have leading female characters who don't start out with an artist told to draw a standard sexy young athelete because marketing.
She is eventually replaced by another character and the plot during the rest of the game is terrible and makes no sense. Such a fun combat game with a lousy story.
