My dad is always dead/missing
Why no dads in AVNs (and erotic stories et al):
1. Less characters to write. If dad lives, he needs to... be present. Respond to what's going on. It's more scenes, renders and text players probably don't care much about.
2. Unless it's an NTR themed game, many players will feel uncomfortable about shagging mom behind dad's back.
3. A dead/missing father can give the MC an excuse to act more mature. He's been through a lot.
4. Finally: the chance to act like the big man of the house and protect all those feeble minded females who are challenged by simple actions like locking the shower door, buying cloths on their own, applying sunscreen, doing yoga on their own, standing up to annoying ex boyfriends etc.
Truth of the matter is that a missing/dead dad is so
helpful in an incest/harem AVN, it's a miracle some AVNs actually have living/present fathers.