Because it is a very simple way to set up the MC of the game. If the father is a dick, it will be easy to explain why the MC is also a dick, and now there is someone to take the blame and make the MC a bit more likeable (in some cases at least). It is also an easy way to have an antagonist in your game. Don't know how to write an epic super villain, with believable motives? Just make the father cock-block the player and you instantly have a villain! It's also makes it easier to break up mom and dad, without the whole family rasing hell, so you can have them all to yourself.