Really? I know that Steam takes 1/3, but I almost every gamer I know uses exclusively Steam for all their games and would be unwilling to go anywhere else to buy or play them, I though that the huge amount of sales from Murder House would've been enough to make him want to put more games there.
I'm guessing that games like this get completely buried under more "popular" stuff on Steam. Here on itch, games like this can flourish and rise to the top much more easily. I buy at itch when I can to better support the dev.